Problem:
Some of our machines are configured with many NVMe devices and
are validated for strict shutdown time requirements. Each NVMe
device plugged into the system, typicaly takes about 4.5 secs
to shutdown. A system with 16 such NVMe devices will takes
approximately 80 secs to shutdown and go through reboot.
The current shutdown APIs as defined at bus level is defined to be
synchronous. Therefore, more devices are in the system the greater
the time it takes to shutdown. This shutdown time significantly
contributes the machine reboot time.
Solution:
This patch set proposes an asynchronous shutdown interface at bus level,
modifies the core driver, device shutdown routine to exploit the
new interface while maintaining backward compatibility with synchronous
implementation already existing (Patch 1 of 3) and exploits new interface
to enable all PCI-E based devices to use asynchronous interface semantics
if necessary (Patch 2 of 3). The implementation at PCI-E level also works
in a backward compatible way, to allow exiting device implementation
to work with current synchronous semantics. Only show cases an example
implementation for NVMe device to exploit this asynchronous shutdown
interface. (Patch 3 of 3).
Changelog:
v2: - Replaced the shutdown_pre & shutdown_post entry point names with the
recommended names (async_shutdown_start and asynch_shutdown_end).
- Comment about ordering requirements between bridge shutdown versus
leaf/endpoint shutdown was agreed to be different when calling
async_shutdown_start and async_shutdown_end. Now this implements the
same order of calling both start and end entry points.
Tanjore Suresh (3):
driver core: Support asynchronous driver shutdown
PCI: Support asynchronous shutdown
nvme: Add async shutdown support
drivers/base/core.c | 38 +++++++++++++++++-
drivers/nvme/host/core.c | 28 +++++++++----
drivers/nvme/host/nvme.h | 8 ++++
drivers/nvme/host/pci.c | 80 ++++++++++++++++++++++++--------------
drivers/pci/pci-driver.c | 20 ++++++++--
include/linux/device/bus.h | 12 ++++++
include/linux/pci.h | 4 ++
7 files changed, 149 insertions(+), 41 deletions(-)
--
2.36.0.rc0.470.gd361397f0d-goog
This changes the bus driver interface with additional entry points
to enable devices to implement asynchronous shutdown. The existing
synchronous interface to shutdown is unmodified and retained for
backward compatibility.
This changes the common device shutdown code to enable devices to
participate in asynchronous shutdown implementation.
Signed-off-by: Tanjore Suresh <[email protected]>
---
drivers/base/core.c | 38 +++++++++++++++++++++++++++++++++++++-
include/linux/device/bus.h | 12 ++++++++++++
2 files changed, 49 insertions(+), 1 deletion(-)
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 3d6430eb0c6a..ba267ae70a22 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -4479,6 +4479,7 @@ EXPORT_SYMBOL_GPL(device_change_owner);
void device_shutdown(void)
{
struct device *dev, *parent;
+ LIST_HEAD(async_shutdown_list);
wait_for_device_probe();
device_block_probing();
@@ -4523,7 +4524,13 @@ void device_shutdown(void)
dev_info(dev, "shutdown_pre\n");
dev->class->shutdown_pre(dev);
}
- if (dev->bus && dev->bus->shutdown) {
+ if (dev->bus && dev->bus->async_shutdown_start) {
+ if (initcall_debug)
+ dev_info(dev, "async_shutdown_start\n");
+ dev->bus->async_shutdown_start(dev);
+ list_add_tail(&dev->kobj.entry,
+ &async_shutdown_list);
+ } else if (dev->bus && dev->bus->shutdown) {
if (initcall_debug)
dev_info(dev, "shutdown\n");
dev->bus->shutdown(dev);
@@ -4543,6 +4550,35 @@ void device_shutdown(void)
spin_lock(&devices_kset->list_lock);
}
spin_unlock(&devices_kset->list_lock);
+
+ /*
+ * Second pass spin for only devices, that have configured
+ * Asynchronous shutdown.
+ */
+ while (!list_empty(&async_shutdown_list)) {
+ dev = list_entry(async_shutdown_list.next, struct device,
+ kobj.entry);
+ parent = get_device(dev->parent);
+ get_device(dev);
+ /*
+ * Make sure the device is off the list
+ */
+ list_del_init(&dev->kobj.entry);
+ if (parent)
+ device_lock(parent);
+ device_lock(dev);
+ if (dev->bus && dev->bus->async_shutdown_end) {
+ if (initcall_debug)
+ dev_info(dev,
+ "async_shutdown_end called\n");
+ dev->bus->async_shutdown_end(dev);
+ }
+ device_unlock(dev);
+ if (parent)
+ device_unlock(parent);
+ put_device(dev);
+ put_device(parent);
+ }
}
/*
diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h
index a039ab809753..f582c9d21515 100644
--- a/include/linux/device/bus.h
+++ b/include/linux/device/bus.h
@@ -49,6 +49,16 @@ struct fwnode_handle;
* will never get called until they do.
* @remove: Called when a device removed from this bus.
* @shutdown: Called at shut-down time to quiesce the device.
+ * @async_shutdown_start: Called at the shutdown-time to start
+ * the shutdown process on the device.
+ * This entry point will be called only
+ * when the bus driver has indicated it would
+ * like to participate in asynchronous shutdown
+ * completion.
+ * @async_shutdown_end: Called at shutdown-time to complete the shutdown
+ * process of the device. This entry point will be called
+ * only when the bus drive has indicated it would like to
+ * participate in the asynchronous shutdown completion.
*
* @online: Called to put the device back online (after offlining it).
* @offline: Called to put the device offline for hot-removal. May fail.
@@ -93,6 +103,8 @@ struct bus_type {
void (*sync_state)(struct device *dev);
void (*remove)(struct device *dev);
void (*shutdown)(struct device *dev);
+ void (*async_shutdown_start)(struct device *dev);
+ void (*async_shutdown_end)(struct device *dev);
int (*online)(struct device *dev);
int (*offline)(struct device *dev);
--
2.36.0.rc0.470.gd361397f0d-goog
On Wed, Apr 13, 2022 at 12:44 AM Tanjore Suresh <[email protected]> wrote:
>
> This changes the bus driver interface with additional entry points
> to enable devices to implement asynchronous shutdown. The existing
> synchronous interface to shutdown is unmodified and retained for
> backward compatibility.
>
> This changes the common device shutdown code to enable devices to
> participate in asynchronous shutdown implementation.
>
> Signed-off-by: Tanjore Suresh <[email protected]>
Is there any specific reason why you didn't follow the design of, say,
dpm_suspend(), where the "async" devices only need to have a flag set
and the driver is not required to implement any new callbacks?
IMO having different driver interfaces for asynchronous suspend and
shutdown would be quite confusing for driver developers, wouldn't it?
> ---
> drivers/base/core.c | 38 +++++++++++++++++++++++++++++++++++++-
> include/linux/device/bus.h | 12 ++++++++++++
> 2 files changed, 49 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 3d6430eb0c6a..ba267ae70a22 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -4479,6 +4479,7 @@ EXPORT_SYMBOL_GPL(device_change_owner);
> void device_shutdown(void)
> {
> struct device *dev, *parent;
> + LIST_HEAD(async_shutdown_list);
>
> wait_for_device_probe();
> device_block_probing();
> @@ -4523,7 +4524,13 @@ void device_shutdown(void)
> dev_info(dev, "shutdown_pre\n");
> dev->class->shutdown_pre(dev);
> }
> - if (dev->bus && dev->bus->shutdown) {
> + if (dev->bus && dev->bus->async_shutdown_start) {
> + if (initcall_debug)
> + dev_info(dev, "async_shutdown_start\n");
> + dev->bus->async_shutdown_start(dev);
> + list_add_tail(&dev->kobj.entry,
> + &async_shutdown_list);
> + } else if (dev->bus && dev->bus->shutdown) {
> if (initcall_debug)
> dev_info(dev, "shutdown\n");
> dev->bus->shutdown(dev);
> @@ -4543,6 +4550,35 @@ void device_shutdown(void)
> spin_lock(&devices_kset->list_lock);
> }
> spin_unlock(&devices_kset->list_lock);
> +
> + /*
> + * Second pass spin for only devices, that have configured
> + * Asynchronous shutdown.
> + */
> + while (!list_empty(&async_shutdown_list)) {
> + dev = list_entry(async_shutdown_list.next, struct device,
> + kobj.entry);
> + parent = get_device(dev->parent);
> + get_device(dev);
> + /*
> + * Make sure the device is off the list
> + */
> + list_del_init(&dev->kobj.entry);
> + if (parent)
> + device_lock(parent);
> + device_lock(dev);
> + if (dev->bus && dev->bus->async_shutdown_end) {
> + if (initcall_debug)
> + dev_info(dev,
> + "async_shutdown_end called\n");
> + dev->bus->async_shutdown_end(dev);
> + }
> + device_unlock(dev);
> + if (parent)
> + device_unlock(parent);
> + put_device(dev);
> + put_device(parent);
> + }
> }
>
> /*
> diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h
> index a039ab809753..f582c9d21515 100644
> --- a/include/linux/device/bus.h
> +++ b/include/linux/device/bus.h
> @@ -49,6 +49,16 @@ struct fwnode_handle;
> * will never get called until they do.
> * @remove: Called when a device removed from this bus.
> * @shutdown: Called at shut-down time to quiesce the device.
> + * @async_shutdown_start: Called at the shutdown-time to start
> + * the shutdown process on the device.
> + * This entry point will be called only
> + * when the bus driver has indicated it would
> + * like to participate in asynchronous shutdown
> + * completion.
> + * @async_shutdown_end: Called at shutdown-time to complete the shutdown
> + * process of the device. This entry point will be called
> + * only when the bus drive has indicated it would like to
> + * participate in the asynchronous shutdown completion.
> *
> * @online: Called to put the device back online (after offlining it).
> * @offline: Called to put the device offline for hot-removal. May fail.
> @@ -93,6 +103,8 @@ struct bus_type {
> void (*sync_state)(struct device *dev);
> void (*remove)(struct device *dev);
> void (*shutdown)(struct device *dev);
> + void (*async_shutdown_start)(struct device *dev);
> + void (*async_shutdown_end)(struct device *dev);
>
> int (*online)(struct device *dev);
> int (*offline)(struct device *dev);
> --
> 2.36.0.rc0.470.gd361397f0d-goog
>
On Tue, Apr 19, 2022 at 03:35:47PM -0700, Tanjore Suresh wrote:
> Hey,
>
> I did not hear any comments on this v2 version. Please help me with your
> comments and approval so that this can be prepared for checkin.
Wait, there was comments, that you seem to have ignored. Why?
A: http://en.wikipedia.org/wiki/Top_post
Q: Were do I find info about this thing called top-posting?
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?
A: No.
Q: Should I include quotations after my reply?
http://daringfireball.net/2007/07/on_top
On Wed, Apr 20, 2022 at 04:12:38PM -0700, Tanjore Suresh wrote:
> Greg,
<snip>
You sent this in html form, which is rejected by our mailing lists.
Please fix up your email client and resend and I will be glad to point
you at this thread on lore.kernel.org with responses from other
developers. Or you can just look it up yourself :)
thanks,
greg k-h
On Tue, Apr 19, 2022 at 03:35:47PM -0700, Tanjore Suresh wrote:
> Hey,
Please never top-post.
> I did not hear any comments on this v2 version. Please help me with your
> comments and approval so that this can be prepared for checkin.
Relax, it is in my to-review queue...
There is no rush here.
greg k-h
On Wed, Apr 20, 2022 at 08:14:37AM +0200, Greg Kroah-Hartman wrote:
> On Tue, Apr 19, 2022 at 03:35:47PM -0700, Tanjore Suresh wrote:
> > Hey,
> >
> > I did not hear any comments on this v2 version. Please help me with your
> > comments and approval so that this can be prepared for checkin.
>
> Wait, there was comments, that you seem to have ignored. Why?
>
Because of that, this patch series is dropped on my end. Please fix up
and resubmit a new version if you still want this.
thanks,
greg k-h
Rafael,
That is a good observation, however, many of the use cases in data
centers (deployment of devices in data centers) do not exploit device
power management. Therefore, I'm not sure that is the right way to
design this.
Also if you look into device_shutdown (drivers/base/core.c) generic
kernel routine does not exploit the shutdown method suggested by you
instead use the generic shutdown methods defined in bus, class,
drivers structures. Therefore, adopting to expand on those generic
shutdown interfaces is the incremental choice to not confuse driver
developers.
Hope this clarifies why this extension is proposed when compared to
overloading a generic shutdown entry point with device power
management requirements.
Thanks
sureshtk
On Fri, Apr 15, 2022 at 7:42 AM Rafael J. Wysocki <[email protected]> wrote:
>
> On Wed, Apr 13, 2022 at 12:44 AM Tanjore Suresh <[email protected]> wrote:
> >
> > This changes the bus driver interface with additional entry points
> > to enable devices to implement asynchronous shutdown. The existing
> > synchronous interface to shutdown is unmodified and retained for
> > backward compatibility.
> >
> > This changes the common device shutdown code to enable devices to
> > participate in asynchronous shutdown implementation.
> >
> > Signed-off-by: Tanjore Suresh <[email protected]>
>
> Is there any specific reason why you didn't follow the design of, say,
> dpm_suspend(), where the "async" devices only need to have a flag set
> and the driver is not required to implement any new callbacks?
>
> IMO having different driver interfaces for asynchronous suspend and
> shutdown would be quite confusing for driver developers, wouldn't it?
>
> > ---
> > drivers/base/core.c | 38 +++++++++++++++++++++++++++++++++++++-
> > include/linux/device/bus.h | 12 ++++++++++++
> > 2 files changed, 49 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index 3d6430eb0c6a..ba267ae70a22 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -4479,6 +4479,7 @@ EXPORT_SYMBOL_GPL(device_change_owner);
> > void device_shutdown(void)
> > {
> > struct device *dev, *parent;
> > + LIST_HEAD(async_shutdown_list);
> >
> > wait_for_device_probe();
> > device_block_probing();
> > @@ -4523,7 +4524,13 @@ void device_shutdown(void)
> > dev_info(dev, "shutdown_pre\n");
> > dev->class->shutdown_pre(dev);
> > }
> > - if (dev->bus && dev->bus->shutdown) {
> > + if (dev->bus && dev->bus->async_shutdown_start) {
> > + if (initcall_debug)
> > + dev_info(dev, "async_shutdown_start\n");
> > + dev->bus->async_shutdown_start(dev);
> > + list_add_tail(&dev->kobj.entry,
> > + &async_shutdown_list);
> > + } else if (dev->bus && dev->bus->shutdown) {
> > if (initcall_debug)
> > dev_info(dev, "shutdown\n");
> > dev->bus->shutdown(dev);
> > @@ -4543,6 +4550,35 @@ void device_shutdown(void)
> > spin_lock(&devices_kset->list_lock);
> > }
> > spin_unlock(&devices_kset->list_lock);
> > +
> > + /*
> > + * Second pass spin for only devices, that have configured
> > + * Asynchronous shutdown.
> > + */
> > + while (!list_empty(&async_shutdown_list)) {
> > + dev = list_entry(async_shutdown_list.next, struct device,
> > + kobj.entry);
> > + parent = get_device(dev->parent);
> > + get_device(dev);
> > + /*
> > + * Make sure the device is off the list
> > + */
> > + list_del_init(&dev->kobj.entry);
> > + if (parent)
> > + device_lock(parent);
> > + device_lock(dev);
> > + if (dev->bus && dev->bus->async_shutdown_end) {
> > + if (initcall_debug)
> > + dev_info(dev,
> > + "async_shutdown_end called\n");
> > + dev->bus->async_shutdown_end(dev);
> > + }
> > + device_unlock(dev);
> > + if (parent)
> > + device_unlock(parent);
> > + put_device(dev);
> > + put_device(parent);
> > + }
> > }
> >
> > /*
> > diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h
> > index a039ab809753..f582c9d21515 100644
> > --- a/include/linux/device/bus.h
> > +++ b/include/linux/device/bus.h
> > @@ -49,6 +49,16 @@ struct fwnode_handle;
> > * will never get called until they do.
> > * @remove: Called when a device removed from this bus.
> > * @shutdown: Called at shut-down time to quiesce the device.
> > + * @async_shutdown_start: Called at the shutdown-time to start
> > + * the shutdown process on the device.
> > + * This entry point will be called only
> > + * when the bus driver has indicated it would
> > + * like to participate in asynchronous shutdown
> > + * completion.
> > + * @async_shutdown_end: Called at shutdown-time to complete the shutdown
> > + * process of the device. This entry point will be called
> > + * only when the bus drive has indicated it would like to
> > + * participate in the asynchronous shutdown completion.
> > *
> > * @online: Called to put the device back online (after offlining it).
> > * @offline: Called to put the device offline for hot-removal. May fail.
> > @@ -93,6 +103,8 @@ struct bus_type {
> > void (*sync_state)(struct device *dev);
> > void (*remove)(struct device *dev);
> > void (*shutdown)(struct device *dev);
> > + void (*async_shutdown_start)(struct device *dev);
> > + void (*async_shutdown_end)(struct device *dev);
> >
> > int (*online)(struct device *dev);
> > int (*offline)(struct device *dev);
> > --
> > 2.36.0.rc0.470.gd361397f0d-goog
> >
On Sat, Apr 30, 2022 at 12:52 AM Greg Kroah-Hartman
<[email protected]> wrote:
>
> A: http://en.wikipedia.org/wiki/Top_post
> Q: Were do I find info about this thing called top-posting?
> A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?
> A: Top-posting.
> Q: What is the most annoying thing in e-mail?
>
> A: No.
> Q: Should I include quotations after my reply?
>
> http://daringfireball.net/2007/07/on_top
>
> On Fri, Apr 29, 2022 at 11:03:07AM -0700, Tanjore Suresh wrote:
> > Rafael,
> >
> > That is a good observation, however, many of the use cases in data
> > centers (deployment of devices in data centers) do not exploit device
> > power management. Therefore, I'm not sure that is the right way to
> > design this.
>
> Yes it is, enable device power management and use that interface please.
> Devices in data centers should of course be doing the same thing as
> everyone else, as it actually saves real money in power costs. To not
> do so is very odd.
>
I guess we are intermixing the terminology of device power management
with shutdown.
My second, third reasoning in my previous e-mail, thought it brings
out that difference. Maybe not.
I will try one more time, my thought process on this one.
This patch is only for shutdown. The shutdown can be done in a system
in various flavors,
(this may include a power being pulled from the system components when
all the devices
are quiescent and it can also be soft shutdown, where power is not
removed from the system, but system
could be attempting a reboot)
The device power management allows the device to bring down any
devices that may be idle to various power states that
device may support in a selective manner & based on the transition
allowed by the device. Such a transition initiated by
the system can be achieved using the 'dpm' interface for runtime power
management (more for extending laptop battery life).
It can also be exploited for system sleep models (suspend and resume -
where state is preserved and restarted from where it left off
--> More applicable for laptops/desktops). That does not mean data
center devices cannot exploit, but they worry about slight latency
variation in any
I/O initiated to any device. Such power management could introduce
more latency when it transitions from one state to another.
Therefore, the use case is more apt for Laptops, in certain cases
desktops in my opinion or understanding.
The shutdown entry point has been traditionally different and the
semantics is that the whole system is going down to a
quiescent state and power may be pulled or may not be, IMO, i am
seeing both are independent requirements, in my view.
Let me know if I am mistaken. I am not sure why we should break the
shutdown semantics as understood by driver developers and
overload it with dpm requirements?
Thanks
sureshtk
> thanks,
>
> greg k-h
A: http://en.wikipedia.org/wiki/Top_post
Q: Were do I find info about this thing called top-posting?
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?
A: No.
Q: Should I include quotations after my reply?
http://daringfireball.net/2007/07/on_top
On Fri, Apr 29, 2022 at 11:03:07AM -0700, Tanjore Suresh wrote:
> Rafael,
>
> That is a good observation, however, many of the use cases in data
> centers (deployment of devices in data centers) do not exploit device
> power management. Therefore, I'm not sure that is the right way to
> design this.
Yes it is, enable device power management and use that interface please.
Devices in data centers should of course be doing the same thing as
everyone else, as it actually saves real money in power costs. To not
do so is very odd.
thanks,
greg k-h
Greg
On Mon, May 2, 2022 at 12:13 PM Tanjore Suresh <[email protected]> wrote:
>
> On Sat, Apr 30, 2022 at 12:52 AM Greg Kroah-Hartman
> <[email protected]> wrote:
> >
> > A: http://en.wikipedia.org/wiki/Top_post
> > Q: Were do I find info about this thing called top-posting?
> > A: Because it messes up the order in which people normally read text.
> > Q: Why is top-posting such a bad thing?
> > A: Top-posting.
> > Q: What is the most annoying thing in e-mail?
> >
> > A: No.
> > Q: Should I include quotations after my reply?
> >
> > http://daringfireball.net/2007/07/on_top
> >
> > On Fri, Apr 29, 2022 at 11:03:07AM -0700, Tanjore Suresh wrote:
> > > Rafael,
> > >
> > > That is a good observation, however, many of the use cases in data
> > > centers (deployment of devices in data centers) do not exploit device
> > > power management. Therefore, I'm not sure that is the right way to
> > > design this.
> >
> > Yes it is, enable device power management and use that interface please.
> > Devices in data centers should of course be doing the same thing as
> > everyone else, as it actually saves real money in power costs. To not
> > do so is very odd.
> >
>
> I guess we are intermixing the terminology of device power management
> with shutdown.
> My second, third reasoning in my previous e-mail, thought it brings
> out that difference. Maybe not.
> I will try one more time, my thought process on this one.
>
> This patch is only for shutdown. The shutdown can be done in a system
> in various flavors,
> (this may include a power being pulled from the system components when
> all the devices
> are quiescent and it can also be soft shutdown, where power is not
> removed from the system, but system
> could be attempting a reboot)
>
> The device power management allows the device to bring down any
> devices that may be idle to various power states that
> device may support in a selective manner & based on the transition
> allowed by the device. Such a transition initiated by
> the system can be achieved using the 'dpm' interface for runtime power
> management (more for extending laptop battery life).
> It can also be exploited for system sleep models (suspend and resume -
> where state is preserved and restarted from where it left off
> --> More applicable for laptops/desktops). That does not mean data
> center devices cannot exploit, but they worry about slight latency
> variation in any
> I/O initiated to any device. Such power management could introduce
> more latency when it transitions from one state to another.
> Therefore, the use case is more apt for Laptops, in certain cases
> desktops in my opinion or understanding.
>
> The shutdown entry point has been traditionally different and the
> semantics is that the whole system is going down to a
> quiescent state and power may be pulled or may not be, IMO, i am
> seeing both are independent requirements, in my view.
> Let me know if I am mistaken. I am not sure why we should break the
> shutdown semantics as understood by driver developers and
> overload it with dpm requirements?
>
I have not seen additional comments, I request your help
in moving this further, please. If i have missed something,
Please let me know.
Thanks
sureshtk
> Thanks
> sureshtk
>
>
> > thanks,
> >
> > greg k-h
On Wed, May 11, 2022 at 02:02:08PM -0700, Tanjore Suresh wrote:
> Greg
>
> On Mon, May 2, 2022 at 12:13 PM Tanjore Suresh <[email protected]> wrote:
> >
> > On Sat, Apr 30, 2022 at 12:52 AM Greg Kroah-Hartman
> > <[email protected]> wrote:
> > >
> > > A: http://en.wikipedia.org/wiki/Top_post
> > > Q: Were do I find info about this thing called top-posting?
> > > A: Because it messes up the order in which people normally read text.
> > > Q: Why is top-posting such a bad thing?
> > > A: Top-posting.
> > > Q: What is the most annoying thing in e-mail?
> > >
> > > A: No.
> > > Q: Should I include quotations after my reply?
> > >
> > > http://daringfireball.net/2007/07/on_top
> > >
> > > On Fri, Apr 29, 2022 at 11:03:07AM -0700, Tanjore Suresh wrote:
> > > > Rafael,
> > > >
> > > > That is a good observation, however, many of the use cases in data
> > > > centers (deployment of devices in data centers) do not exploit device
> > > > power management. Therefore, I'm not sure that is the right way to
> > > > design this.
> > >
> > > Yes it is, enable device power management and use that interface please.
> > > Devices in data centers should of course be doing the same thing as
> > > everyone else, as it actually saves real money in power costs. To not
> > > do so is very odd.
> > >
> >
> > I guess we are intermixing the terminology of device power management
> > with shutdown.
> > My second, third reasoning in my previous e-mail, thought it brings
> > out that difference. Maybe not.
> > I will try one more time, my thought process on this one.
> >
> > This patch is only for shutdown. The shutdown can be done in a system
> > in various flavors,
> > (this may include a power being pulled from the system components when
> > all the devices
> > are quiescent and it can also be soft shutdown, where power is not
> > removed from the system, but system
> > could be attempting a reboot)
> >
> > The device power management allows the device to bring down any
> > devices that may be idle to various power states that
> > device may support in a selective manner & based on the transition
> > allowed by the device. Such a transition initiated by
> > the system can be achieved using the 'dpm' interface for runtime power
> > management (more for extending laptop battery life).
> > It can also be exploited for system sleep models (suspend and resume -
> > where state is preserved and restarted from where it left off
> > --> More applicable for laptops/desktops). That does not mean data
> > center devices cannot exploit, but they worry about slight latency
> > variation in any
> > I/O initiated to any device. Such power management could introduce
> > more latency when it transitions from one state to another.
> > Therefore, the use case is more apt for Laptops, in certain cases
> > desktops in my opinion or understanding.
> >
> > The shutdown entry point has been traditionally different and the
> > semantics is that the whole system is going down to a
> > quiescent state and power may be pulled or may not be, IMO, i am
> > seeing both are independent requirements, in my view.
> > Let me know if I am mistaken. I am not sure why we should break the
> > shutdown semantics as understood by driver developers and
> > overload it with dpm requirements?
> >
>
> I have not seen additional comments, I request your help
> in moving this further, please. If i have missed something,
> Please let me know.
Please rebase and resubmit your series with the extra information you
have provided here in the changelog text so we can review it again. The
patch series is long gone from my queue, sorry.
thanks,
greg k-h