Tasklets have long been deprecated as being too heavy on the system
by running in irq context - and this is not a performance critical
path. If a higher priority process wants to run, it must wait for
the tasklet to finish before doing so.
c67x00_do_work() will now run in process context and have further
concurrency (tasklets being serialized among themselves), but this
is done holding the c67x00->lock, so it should be fine. Furthermore,
this patch fixes the usage of the lock in the callback as otherwise
it would need to be irq-safe.
Signed-off-by: Davidlohr Bueso <[email protected]>
---
drivers/usb/c67x00/c67x00-hcd.h | 2 +-
drivers/usb/c67x00/c67x00-sched.c | 12 +++++++-----
2 files changed, 8 insertions(+), 6 deletions(-)
diff --git a/drivers/usb/c67x00/c67x00-hcd.h b/drivers/usb/c67x00/c67x00-hcd.h
index 6b6b04a3fe0f..6332a6b5dce6 100644
--- a/drivers/usb/c67x00/c67x00-hcd.h
+++ b/drivers/usb/c67x00/c67x00-hcd.h
@@ -76,7 +76,7 @@ struct c67x00_hcd {
u16 next_td_addr;
u16 next_buf_addr;
- struct tasklet_struct tasklet;
+ struct work_struct work;
struct completion endpoint_disable;
diff --git a/drivers/usb/c67x00/c67x00-sched.c b/drivers/usb/c67x00/c67x00-sched.c
index e65f1a0ae80b..af60f4fdd340 100644
--- a/drivers/usb/c67x00/c67x00-sched.c
+++ b/drivers/usb/c67x00/c67x00-sched.c
@@ -1123,24 +1123,26 @@ static void c67x00_do_work(struct c67x00_hcd *c67x00)
/* -------------------------------------------------------------------------- */
-static void c67x00_sched_tasklet(struct tasklet_struct *t)
+static void c67x00_sched_work(struct work_struct *work)
{
- struct c67x00_hcd *c67x00 = from_tasklet(c67x00, t, tasklet);
+ struct c67x00_hcd *c67x00;
+
+ c67x00 = container_of(work, struct c67x00_hcd, work);
c67x00_do_work(c67x00);
}
void c67x00_sched_kick(struct c67x00_hcd *c67x00)
{
- tasklet_hi_schedule(&c67x00->tasklet);
+ queue_work(system_highpri_wq, &c67x00->work);
}
int c67x00_sched_start_scheduler(struct c67x00_hcd *c67x00)
{
- tasklet_setup(&c67x00->tasklet, c67x00_sched_tasklet);
+ INIT_WORK(&c67x00->work, c67x00_sched_work);
return 0;
}
void c67x00_sched_stop_scheduler(struct c67x00_hcd *c67x00)
{
- tasklet_kill(&c67x00->tasklet);
+ cancel_work_sync(&c67x00->work);
}
--
2.26.2
Hello!
On 11.01.2021 7:40, Davidlohr Bueso wrote:
> Tasklets have long been deprecated as being too heavy on the system
> by running in irq context - and this is not a performance critical
> path. If a higher priority process wants to run, it must wait for
> the tasklet to finish before doing so.
>
> c67x00_do_work() will now run in process context and have further
> concurrency (tasklets being serialized among themselves), but this
> is done holding the c67x00->lock, so it should be fine. Furthermore,
> this patch fixes the usage of the lock in the callback as otherwise
> it would need to be irq-safe.
>
> Signed-off-by: Davidlohr Bueso <[email protected]>
[...]
> diff --git a/drivers/usb/c67x00/c67x00-sched.c b/drivers/usb/c67x00/c67x00-sched.c
> index e65f1a0ae80b..af60f4fdd340 100644
> --- a/drivers/usb/c67x00/c67x00-sched.c
> +++ b/drivers/usb/c67x00/c67x00-sched.c
> @@ -1123,24 +1123,26 @@ static void c67x00_do_work(struct c67x00_hcd *c67x00)
>
> /* -------------------------------------------------------------------------- */
>
> -static void c67x00_sched_tasklet(struct tasklet_struct *t)
> +static void c67x00_sched_work(struct work_struct *work)
> {
> - struct c67x00_hcd *c67x00 = from_tasklet(c67x00, t, tasklet);
> + struct c67x00_hcd *c67x00;
> +
> + c67x00 = container_of(work, struct c67x00_hcd, work);
> c67x00_do_work(c67x00);
> }
>
> void c67x00_sched_kick(struct c67x00_hcd *c67x00)
> {
> - tasklet_hi_schedule(&c67x00->tasklet);
> + queue_work(system_highpri_wq, &c67x00->work);
Use a tab to indent, please.
> }
>
> int c67x00_sched_start_scheduler(struct c67x00_hcd *c67x00)
> {
> - tasklet_setup(&c67x00->tasklet, c67x00_sched_tasklet);
> + INIT_WORK(&c67x00->work, c67x00_sched_work);
Here as well.
> return 0;
> }
>
> void c67x00_sched_stop_scheduler(struct c67x00_hcd *c67x00)
> {
> - tasklet_kill(&c67x00->tasklet);
> + cancel_work_sync(&c67x00->work);
And here.
[...]
MBR, Sergei
On Mon, 11 Jan 2021, Hillf Danton wrote:
>On Sun, 10 Jan 2021 20:40:50 -0800 Davidlohr Bueso wrote:
>> Tasklets have long been deprecated as being too heavy on the system
>> by running in irq context - and this is not a performance critical
>> path. If a higher priority process wants to run, it must wait for
>> the tasklet to finish before doing so.
>>
>> c67x00_do_work() will now run in process context and have further
>> concurrency (tasklets being serialized among themselves), but this
>> is done holding the c67x00->lock, so it should be fine. Furthermore,
>> this patch fixes the usage of the lock in the callback as otherwise
>> it would need to be irq-safe.
>
>Can you add a couple of words about the need to be irq-safe because
>no lock is taken for scheduling either tasklet or work?
I was refering to the locking in the c67x00_do_work() tasklet callback.
Because it is currently under irq it should be disabling irq (or at least
BH) but after this patch that is no longer the case.
>>
>> Signed-off-by: Davidlohr Bueso <[email protected]>
>> ---
>> drivers/usb/c67x00/c67x00-hcd.h | 2 +-
>> drivers/usb/c67x00/c67x00-sched.c | 12 +++++++-----
>> 2 files changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/usb/c67x00/c67x00-hcd.h b/drivers/usb/c67x00/c67x00-hcd.h
>> index 6b6b04a3fe0f..6332a6b5dce6 100644
>> --- a/drivers/usb/c67x00/c67x00-hcd.h
>> +++ b/drivers/usb/c67x00/c67x00-hcd.h
>> @@ -76,7 +76,7 @@ struct c67x00_hcd {
>> u16 next_td_addr;
>> u16 next_buf_addr;
>>
>> - struct tasklet_struct tasklet;
>> + struct work_struct work;
>>
>> struct completion endpoint_disable;
>>
>> diff --git a/drivers/usb/c67x00/c67x00-sched.c b/drivers/usb/c67x00/c67x00-sched.c
>> index e65f1a0ae80b..af60f4fdd340 100644
>> --- a/drivers/usb/c67x00/c67x00-sched.c
>> +++ b/drivers/usb/c67x00/c67x00-sched.c
>> @@ -1123,24 +1123,26 @@ static void c67x00_do_work(struct c67x00_hcd *c67x00)
>>
>> /* -------------------------------------------------------------------------- */
>>
>> -static void c67x00_sched_tasklet(struct tasklet_struct *t)
>> +static void c67x00_sched_work(struct work_struct *work)
>> {
>> - struct c67x00_hcd *c67x00 = from_tasklet(c67x00, t, tasklet);
>> + struct c67x00_hcd *c67x00;
>> +
>> + c67x00 = container_of(work, struct c67x00_hcd, work);
>> c67x00_do_work(c67x00);
>> }
>>
>> void c67x00_sched_kick(struct c67x00_hcd *c67x00)
>> {
>> - tasklet_hi_schedule(&c67x00->tasklet);
>> + queue_work(system_highpri_wq, &c67x00->work);
>
>Better if one line comment is added for highpri, given this is not a
>performance critical path.
I'm not sure the value here, considering the highprio is not being
changed here. There are a few drivers who use highpri workqueue and
care about latencies but they are still not performance critical (to
the overall system that is, which is what I meant by that).
Thanks,
Davidlohr