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authorChengming Zhou <zhouchengming@bytedance.com>2022-04-08 15:19:14 +0300
committerPeter Zijlstra <peterz@infradead.org>2022-04-22 13:14:08 +0300
commit890d550d7dbac7a31ecaa78732aa22be282bb6b8 (patch)
tree5a138de8963eaf8e0f2e58bafb913e309fde0b68 /Documentation
parent0a00a354644ee1800d31c47cf5927b9b50272fac (diff)
downloadlinux-890d550d7dbac7a31ecaa78732aa22be282bb6b8.tar.xz
sched/psi: report zeroes for CPU full at the system level
Martin find it confusing when look at the /proc/pressure/cpu output, and found no hint about that CPU "full" line in psi Documentation. % cat /proc/pressure/cpu some avg10=0.92 avg60=0.91 avg300=0.73 total=933490489 full avg10=0.22 avg60=0.23 avg300=0.16 total=358783277 The PSI_CPU_FULL state is introduced by commit e7fcd7622823 ("psi: Add PSI_CPU_FULL state"), which mainly for cgroup level, but also counted at the system level as a side effect. Naturally, the FULL state doesn't exist for the CPU resource at the system level. These "full" numbers can come from CPU idle schedule latency. For example, t1 is the time when task wakeup on an idle CPU, t2 is the time when CPU pick and switch to it. The delta of (t2 - t1) will be in CPU_FULL state. Another case all processes can be stalled is when all cgroups have been throttled at the same time, which unlikely to happen. Anyway, CPU_FULL metric is meaningless and confusing at the system level. So this patch will report zeroes for CPU full at the system level, and update psi Documentation accordingly. Fixes: e7fcd7622823 ("psi: Add PSI_CPU_FULL state") Reported-by: Martin Steigerwald <Martin.Steigerwald@proact.de> Suggested-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Link: https://lore.kernel.org/r/20220408121914.82855-1-zhouchengming@bytedance.com
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/accounting/psi.rst9
1 files changed, 4 insertions, 5 deletions
diff --git a/Documentation/accounting/psi.rst b/Documentation/accounting/psi.rst
index 860fe651d645..5e40b3f437f9 100644
--- a/Documentation/accounting/psi.rst
+++ b/Documentation/accounting/psi.rst
@@ -37,11 +37,7 @@ Pressure interface
Pressure information for each resource is exported through the
respective file in /proc/pressure/ -- cpu, memory, and io.
-The format for CPU is as such::
-
- some avg10=0.00 avg60=0.00 avg300=0.00 total=0
-
-and for memory and IO::
+The format is as such::
some avg10=0.00 avg60=0.00 avg300=0.00 total=0
full avg10=0.00 avg60=0.00 avg300=0.00 total=0
@@ -58,6 +54,9 @@ situation from a state where some tasks are stalled but the CPU is
still doing productive work. As such, time spent in this subset of the
stall state is tracked separately and exported in the "full" averages.
+CPU full is undefined at the system level, but has been reported
+since 5.13, so it is set to zero for backward compatibility.
+
The ratios (in %) are tracked as recent trends over ten, sixty, and
three hundred second windows, which gives insight into short term events
as well as medium and long term trends. The total absolute stall time