MBA software controller (mba_sc) is a feedback loop which periodically
reads MBM counters and tries to restrict the bandwidth below a user
specified bandwidth. It tags along MBM counter overflow handler to do
the updates with 1s interval in mbm_update() and update_mba_bw().
The purpose of mbm_update() is to periodically read the MBM counters to
make sure that the hardware counter doesn't wrap around more than once
between user samplings. mbm_update() calls __mon_event_count() for local
bandwidth updating when mba_sc is not enabled, but calls mbm_bw_count()
instead when mba_sc is enabled. __mon_event_count() will not be called
for local bandwidth updating in MBM counter overflow handler, but it is
still called when reading MBM local bandwidth counter file
'mbm_local_bytes', the call path is as below:
rdtgroup_mondata_show()
mon_event_read()
mon_event_count()
__mon_event_count()
In __mon_event_count(), m->chunks is updated by delta chunks which is
calculated from previous MSR value (m->prev_msr) and current MSR value.
When mba_sc is enabled, m->chunks is also updated in mbm_update() by
mistake by the delta chunks which is calculated from m->prev_bw_msr
instead of m->prev_msr. But m->chunks is not used in update_mba_bw() in
the mba_sc feedback loop.
When reading MBM local bandwidth counter file, m->chunks was changed
unexpectedly by mbm_bw_count(). As a result, the incorrect local
bandwidth counter which calculated from incorrect m->chunks is read out
to the user.
Fix this by removing incorrect m->chunks updating in mbm_bw_count() in
MBM counter overflow handler, and always calling __mon_event_count() in
mbm_update() to make sure that the hardware local bandwidth counter
doesn't wrap around.
Test steps:
# Run workload with aggressive memory bandwidth (e.g., 10 GB/s)
git clone https://github.com/intel/intel-cmt-cat && cd intel-cmt-cat
&& make
./tools/membw/membw -c 0 -b 10000 --read
# Enable MBA software controller
mount -t resctrl resctrl -o mba_MBps /sys/fs/resctrl
# Create control group c1
mkdir /sys/fs/resctrl/c1
# Set MB throttle to 6 GB/s
echo "MB:0=6000;1=6000" > /sys/fs/resctrl/c1/schemata
# Write PID of the workload to tasks file
echo `pidof membw` > /sys/fs/resctrl/c1/tasks
# Read local bytes counters twice with 1s interval, the calculated
# local bandwidth is not as expected (approaching to 6 GB/s):
local_1=`cat /sys/fs/resctrl/c1/mon_data/mon_L3_00/mbm_local_bytes`
sleep 1
local_2=`cat /sys/fs/resctrl/c1/mon_data/mon_L3_00/mbm_local_bytes`
echo "local b/w (bytes/s):" `expr $local_2 - $local_1`
Before fix:
local b/w (bytes/s): 11076796416
After fix:
local b/w (bytes/s): 5465014272
Fixes: ba0f26d8529c (x86/intel_rdt/mba_sc: Prepare for feedback loop)
Signed-off-by: Xiaochen Shen <[email protected]>
Reviewed-by: Tony Luck <[email protected]>
---
arch/x86/kernel/cpu/resctrl/monitor.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 54dffe574e67..a98519a3a2e6 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -279,7 +279,6 @@ static void mbm_bw_count(u32 rmid, struct rmid_read *rr)
return;
chunks = mbm_overflow_count(m->prev_bw_msr, tval, rr->r->mbm_width);
- m->chunks += chunks;
cur_bw = (chunks * r->mon_scale) >> 20;
if (m->delta_comp)
@@ -450,15 +449,14 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d, int rmid)
}
if (is_mbm_local_enabled()) {
rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
+ __mon_event_count(rmid, &rr);
/*
* Call the MBA software controller only for the
* control groups and when user has enabled
* the software controller explicitly.
*/
- if (!is_mba_sc(NULL))
- __mon_event_count(rmid, &rr);
- else
+ if (is_mba_sc(NULL))
mbm_bw_count(rmid, &rr);
}
}
--
1.8.3.1
The following commit has been merged into the x86/cache branch of tip:
Commit-ID: 2ba836dbe2467d31fffb439258c2f454c6f1a317
Gitweb: https://git.kernel.org/tip/2ba836dbe2467d31fffb439258c2f454c6f1a317
Author: Xiaochen Shen <[email protected]>
AuthorDate: Fri, 04 Dec 2020 14:27:59 +08:00
Committer: Borislav Petkov <[email protected]>
CommitterDate: Wed, 09 Dec 2020 20:00:46 +01:00
x86/resctrl: Fix incorrect local bandwidth when mba_sc is enabled
The MBA software controller (mba_sc) is a feedback loop which periodically
reads MBM counters and tries to restrict the bandwidth below a user
specified bandwidth. It tags along the MBM counter overflow handler to do
the updates with 1s interval in mbm_update() and update_mba_bw().
The purpose of mbm_update() is to periodically read the MBM counters to
make sure that the hardware counter doesn't wrap around more than once
between user samplings. mbm_update() calls __mon_event_count() for local
bandwidth updating when mba_sc is not enabled, but calls mbm_bw_count()
instead when mba_sc is enabled. __mon_event_count() will not be called
for local bandwidth updating in MBM counter overflow handler, but it is
still called when reading MBM local bandwidth counter file
'mbm_local_bytes', the call path is as below:
rdtgroup_mondata_show()
mon_event_read()
mon_event_count()
__mon_event_count()
In __mon_event_count(), m->chunks is updated by delta chunks which is
calculated from previous MSR value (m->prev_msr) and current MSR value.
When mba_sc is enabled, m->chunks is also updated in mbm_update() by
mistake by the delta chunks which is calculated from m->prev_bw_msr
instead of m->prev_msr. But m->chunks is not used in update_mba_bw() in
the mba_sc feedback loop.
When reading MBM local bandwidth counter file, m->chunks was changed
unexpectedly by mbm_bw_count(). As a result, the incorrect local
bandwidth counter which calculated using incorrect m->chunks is shown to
the user.
Fix this by removing incorrect m->chunks updating in mbm_bw_count() in
MBM counter overflow handler, and always calling __mon_event_count() in
mbm_update() to make sure that the hardware local bandwidth counter
doesn't wrap around.
Test steps:
# Run workload with aggressive memory bandwidth (e.g., 10 GB/s)
git clone https://github.com/intel/intel-cmt-cat && cd intel-cmt-cat
&& make
./tools/membw/membw -c 0 -b 10000 --read
# Enable MBA software controller
mount -t resctrl resctrl -o mba_MBps /sys/fs/resctrl
# Create control group c1
mkdir /sys/fs/resctrl/c1
# Set MB throttle to 6 GB/s
echo "MB:0=6000;1=6000" > /sys/fs/resctrl/c1/schemata
# Write PID of the workload to tasks file
echo `pidof membw` > /sys/fs/resctrl/c1/tasks
# Read local bytes counters twice with 1s interval, the calculated
# local bandwidth is not as expected (approaching to 6 GB/s):
local_1=`cat /sys/fs/resctrl/c1/mon_data/mon_L3_00/mbm_local_bytes`
sleep 1
local_2=`cat /sys/fs/resctrl/c1/mon_data/mon_L3_00/mbm_local_bytes`
echo "local b/w (bytes/s):" `expr $local_2 - $local_1`
Before fix:
local b/w (bytes/s): 11076796416
After fix:
local b/w (bytes/s): 5465014272
Fixes: ba0f26d8529c (x86/intel_rdt/mba_sc: Prepare for feedback loop)
Signed-off-by: Xiaochen Shen <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Reviewed-by: Tony Luck <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
---
arch/x86/kernel/cpu/resctrl/monitor.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 622073f..93a33b7 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -320,7 +320,6 @@ static int __mon_event_count(u32 rmid, struct rmid_read *rr)
}
chunks = mbm_overflow_count(m->prev_msr, tval, rr->r->mbm_width);
- m->chunks += chunks;
m->prev_msr = tval;
rr->val += get_corrected_mbm_count(rmid, m->chunks);
@@ -514,15 +513,14 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d, int rmid)
}
if (is_mbm_local_enabled()) {
rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
+ __mon_event_count(rmid, &rr);
/*
* Call the MBA software controller only for the
* control groups and when user has enabled
* the software controller explicitly.
*/
- if (!is_mba_sc(NULL))
- __mon_event_count(rmid, &rr);
- else
+ if (is_mba_sc(NULL))
mbm_bw_count(rmid, &rr);
}
}
On Wed, Dec 09, 2020 at 11:23:28PM +0100, Borislav Petkov wrote:
> and you should remove the chunks assignment too.
Yah, ignore that part - mbm_bw_count() does need chunks for cur_bw. Oh
well.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
On Wed, Dec 09, 2020 at 07:06:58PM -0000, tip-bot2 for Xiaochen Shen wrote:
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 622073f..93a33b7 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -320,7 +320,6 @@ static int __mon_event_count(u32 rmid, struct rmid_read *rr)
> }
>
> chunks = mbm_overflow_count(m->prev_msr, tval, rr->r->mbm_width);
> - m->chunks += chunks;
> m->prev_msr = tval;
>
> rr->val += get_corrected_mbm_count(rmid, m->chunks);
Hmm, zapping this one. First, there's an unused variable warning:
https://lkml.kernel.org/r/[email protected]
and you should remove the chunks assignment too.
And then it didn't apply cleanly:
$ test-apply.sh /tmp/xiaochen.01
checking file arch/x86/kernel/cpu/resctrl/monitor.c
Hunk #1 FAILED at 279.
Hunk #2 succeeded at 514 (offset 64 lines).
1 out of 2 hunks FAILED
I wiggled it in but it ended up removing the wrong chunks inc line -
not the one in mbm_bw_count() but in __mon_event_count() - which I just
realized.
So please redo this patch against:
https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/log/?h=x86/cache
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
Hi Boris,
On 12/10/2020 6:23, Borislav Petkov wrote:
> And then it didn't apply cleanly:
>
> $ test-apply.sh /tmp/xiaochen.01
> checking file arch/x86/kernel/cpu/resctrl/monitor.c
> Hunk #1 FAILED at 279.
> Hunk #2 succeeded at 514 (offset 64 lines).
> 1 out of 2 hunks FAILED
>
> I wiggled it in but it ended up removing the wrong chunks inc line -
> not the one in mbm_bw_count() but in __mon_event_count() - which I just
> realized.
Thank you for clarifying this issue. It is not a 0-DAY CI issue.
>
> So please redo this patch against:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/log/?h=x86/cache
>
> Thx.
I will send a patch against branch tip: x86/cache soon.
Thank you.
--
Best regards,
Xiaochen
MBA software controller (mba_sc) is a feedback loop which periodically
reads MBM counters and tries to restrict the bandwidth below a user
specified bandwidth. It tags along MBM counter overflow handler to do
the updates with 1s interval in mbm_update() and update_mba_bw().
The purpose of mbm_update() is to periodically read the MBM counters to
make sure that the hardware counter doesn't wrap around more than once
between user samplings. mbm_update() calls __mon_event_count() for local
bandwidth updating when mba_sc is not enabled, but calls mbm_bw_count()
instead when mba_sc is enabled. __mon_event_count() will not be called
for local bandwidth updating in MBM counter overflow handler, but it is
still called when reading MBM local bandwidth counter file
'mbm_local_bytes', the call path is as below:
rdtgroup_mondata_show()
mon_event_read()
mon_event_count()
__mon_event_count()
In __mon_event_count(), m->chunks is updated by delta chunks which is
calculated from previous MSR value (m->prev_msr) and current MSR value.
When mba_sc is enabled, m->chunks is also updated in mbm_update() by
mistake by the delta chunks which is calculated from m->prev_bw_msr
instead of m->prev_msr. But m->chunks is not used in update_mba_bw() in
the mba_sc feedback loop.
When reading MBM local bandwidth counter file, m->chunks was changed
unexpectedly by mbm_bw_count(). As a result, the incorrect local
bandwidth counter which calculated from incorrect m->chunks is read out
to the user.
Fix this by removing incorrect m->chunks updating in mbm_bw_count() in
MBM counter overflow handler, and always calling __mon_event_count() in
mbm_update() to make sure that the hardware local bandwidth counter
doesn't wrap around.
Test steps:
# Run workload with aggressive memory bandwidth (e.g., 10 GB/s)
git clone https://github.com/intel/intel-cmt-cat && cd intel-cmt-cat
&& make
./tools/membw/membw -c 0 -b 10000 --read
# Enable MBA software controller
mount -t resctrl resctrl -o mba_MBps /sys/fs/resctrl
# Create control group c1
mkdir /sys/fs/resctrl/c1
# Set MB throttle to 6 GB/s
echo "MB:0=6000;1=6000" > /sys/fs/resctrl/c1/schemata
# Write PID of the workload to tasks file
echo `pidof membw` > /sys/fs/resctrl/c1/tasks
# Read local bytes counters twice with 1s interval, the calculated
# local bandwidth is not as expected (approaching to 6 GB/s):
local_1=`cat /sys/fs/resctrl/c1/mon_data/mon_L3_00/mbm_local_bytes`
sleep 1
local_2=`cat /sys/fs/resctrl/c1/mon_data/mon_L3_00/mbm_local_bytes`
echo "local b/w (bytes/s):" `expr $local_2 - $local_1`
Before fix:
local b/w (bytes/s): 11076796416
After fix:
local b/w (bytes/s): 5465014272
Fixes: ba0f26d8529c (x86/intel_rdt/mba_sc: Prepare for feedback loop)
Signed-off-by: Xiaochen Shen <[email protected]>
Reviewed-by: Tony Luck <[email protected]>
---
arch/x86/kernel/cpu/resctrl/monitor.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 622073f..7ac3121 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -343,7 +343,6 @@ static void mbm_bw_count(u32 rmid, struct rmid_read *rr)
return;
chunks = mbm_overflow_count(m->prev_bw_msr, tval, rr->r->mbm_width);
- m->chunks += chunks;
cur_bw = (get_corrected_mbm_count(rmid, chunks) * r->mon_scale) >> 20;
if (m->delta_comp)
@@ -514,15 +513,14 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d, int rmid)
}
if (is_mbm_local_enabled()) {
rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
+ __mon_event_count(rmid, &rr);
/*
* Call the MBA software controller only for the
* control groups and when user has enabled
* the software controller explicitly.
*/
- if (!is_mba_sc(NULL))
- __mon_event_count(rmid, &rr);
- else
+ if (is_mba_sc(NULL))
mbm_bw_count(rmid, &rr);
}
}
--
1.8.3.1
On Thu, Dec 10, 2020 at 12:45:11PM +0800, Xiaochen Shen wrote:
> Thank you for clarifying this issue. It is not a 0-DAY CI issue.
Which begs the question: this patch should be Cc: stable and should go
in now, shouldn't it?
Because then the first submission applies cleanly ontop of
tip:x86/urgent.
I mean, it is fixing only reporting but that reporting is kinda waaay
off.
Hmmm?
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
Hi Boris,
On 12/10/2020 18:26, Borislav Petkov wrote:
> On Thu, Dec 10, 2020 at 12:45:11PM +0800, Xiaochen Shen wrote:
>> Thank you for clarifying this issue. It is not a 0-DAY CI issue.
> Which begs the question: this patch should be Cc: stable and should go
> in now, shouldn't it?
>
> Because then the first submission applies cleanly ontop of
> tip:x86/urgent.
>
> I mean, it is fixing only reporting but that reporting is kinda waaay
> off.
>
> Hmmm?
>
Yes. Thank you for pointing out this, we'd better add Cc: stable tag.
But we have to backport the patch for -stable trees because the code base
is changed by following upstream commits:
(1) For all stable trees: in commit abe8f12b4425 ("x86/resctrl: Remove
unused struct mbm_state::chunks_bw"), removing unused struct
mbm_state::chunks_bw changes the code base for this patch.
(2) For 4.14 and 4.19 stable trees: in commit fa7d949337cc ("x86/resctrl:
Rename and move rdt files to a separate directory"), the file
arch/x86/kernel/cpu/intel_rdt_monitor.c has been renamed and moved to
arch/x86/kernel/cpu/resctrl/monitor.c. This patch needs to be rebased.
I plan to do backporting for all -stable trees after this patch is merged
into upstream.
Thank you.
--
Best regards,
Xiaochen
On Fri, Dec 11, 2020 at 12:40:46AM +0800, Xiaochen Shen wrote:
> I plan to do backporting for all -stable trees after this patch is merged
> into upstream.
Ok, you can do that when Greg sends the mails that it cannot apply to
the respective trees. Lemme queue this one to urgent now.
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: 06c5fe9b12dde1b62821f302f177c972bb1c81f9
Gitweb: https://git.kernel.org/tip/06c5fe9b12dde1b62821f302f177c972bb1c81f9
Author: Xiaochen Shen <[email protected]>
AuthorDate: Fri, 04 Dec 2020 14:27:59 +08:00
Committer: Borislav Petkov <[email protected]>
CommitterDate: Thu, 10 Dec 2020 17:52:37 +01:00
x86/resctrl: Fix incorrect local bandwidth when mba_sc is enabled
The MBA software controller (mba_sc) is a feedback loop which
periodically reads MBM counters and tries to restrict the bandwidth
below a user-specified value. It tags along the MBM counter overflow
handler to do the updates with 1s interval in mbm_update() and
update_mba_bw().
The purpose of mbm_update() is to periodically read the MBM counters to
make sure that the hardware counter doesn't wrap around more than once
between user samplings. mbm_update() calls __mon_event_count() for local
bandwidth updating when mba_sc is not enabled, but calls mbm_bw_count()
instead when mba_sc is enabled. __mon_event_count() will not be called
for local bandwidth updating in MBM counter overflow handler, but it is
still called when reading MBM local bandwidth counter file
'mbm_local_bytes', the call path is as below:
rdtgroup_mondata_show()
mon_event_read()
mon_event_count()
__mon_event_count()
In __mon_event_count(), m->chunks is updated by delta chunks which is
calculated from previous MSR value (m->prev_msr) and current MSR value.
When mba_sc is enabled, m->chunks is also updated in mbm_update() by
mistake by the delta chunks which is calculated from m->prev_bw_msr
instead of m->prev_msr. But m->chunks is not used in update_mba_bw() in
the mba_sc feedback loop.
When reading MBM local bandwidth counter file, m->chunks was changed
unexpectedly by mbm_bw_count(). As a result, the incorrect local
bandwidth counter which calculated from incorrect m->chunks is shown to
the user.
Fix this by removing incorrect m->chunks updating in mbm_bw_count() in
MBM counter overflow handler, and always calling __mon_event_count() in
mbm_update() to make sure that the hardware local bandwidth counter
doesn't wrap around.
Test steps:
# Run workload with aggressive memory bandwidth (e.g., 10 GB/s)
git clone https://github.com/intel/intel-cmt-cat && cd intel-cmt-cat
&& make
./tools/membw/membw -c 0 -b 10000 --read
# Enable MBA software controller
mount -t resctrl resctrl -o mba_MBps /sys/fs/resctrl
# Create control group c1
mkdir /sys/fs/resctrl/c1
# Set MB throttle to 6 GB/s
echo "MB:0=6000;1=6000" > /sys/fs/resctrl/c1/schemata
# Write PID of the workload to tasks file
echo `pidof membw` > /sys/fs/resctrl/c1/tasks
# Read local bytes counters twice with 1s interval, the calculated
# local bandwidth is not as expected (approaching to 6 GB/s):
local_1=`cat /sys/fs/resctrl/c1/mon_data/mon_L3_00/mbm_local_bytes`
sleep 1
local_2=`cat /sys/fs/resctrl/c1/mon_data/mon_L3_00/mbm_local_bytes`
echo "local b/w (bytes/s):" `expr $local_2 - $local_1`
Before fix:
local b/w (bytes/s): 11076796416
After fix:
local b/w (bytes/s): 5465014272
Fixes: ba0f26d8529c (x86/intel_rdt/mba_sc: Prepare for feedback loop)
Signed-off-by: Xiaochen Shen <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Reviewed-by: Tony Luck <[email protected]>
Cc: <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
---
arch/x86/kernel/cpu/resctrl/monitor.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 54dffe5..a98519a 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -279,7 +279,6 @@ static void mbm_bw_count(u32 rmid, struct rmid_read *rr)
return;
chunks = mbm_overflow_count(m->prev_bw_msr, tval, rr->r->mbm_width);
- m->chunks += chunks;
cur_bw = (chunks * r->mon_scale) >> 20;
if (m->delta_comp)
@@ -450,15 +449,14 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d, int rmid)
}
if (is_mbm_local_enabled()) {
rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
+ __mon_event_count(rmid, &rr);
/*
* Call the MBA software controller only for the
* control groups and when user has enabled
* the software controller explicitly.
*/
- if (!is_mba_sc(NULL))
- __mon_event_count(rmid, &rr);
- else
+ if (is_mba_sc(NULL))
mbm_bw_count(rmid, &rr);
}
}