On 2022/3/3 9:26 下午, Johannes Weiner wrote:
> On Thu, Mar 03, 2022 at 01:58:14PM +0800, Chengming Zhou wrote:
>> 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 removed CPU full metric at the
>> system level, and removed it's monitor function too. The psi
>> Documentation has also been updated accordingly.
>>
>> Fixes: e7fcd7622823 ("psi: Add PSI_CPU_FULL state")
>> Reported-by: Martin Steigerwald <Martin.Steigerwald@xxxxxxxxx>
>> Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
>> ---
>> Documentation/accounting/psi.rst | 18 +++++++++++++++---
>> kernel/sched/psi.c | 10 +++++++++-
>> 2 files changed, 24 insertions(+), 4 deletions(-)
>>
>> diff --git a/Documentation/accounting/psi.rst b/Documentation/accounting/psi.rst
>> index 860fe651d645..519652c06d7d 100644
>> --- a/Documentation/accounting/psi.rst
>> +++ b/Documentation/accounting/psi.rst
>> @@ -178,8 +178,20 @@ Cgroup2 interface
>> In a system with a CONFIG_CGROUP=y kernel and the cgroup2 filesystem
>> mounted, pressure stall information is also tracked for tasks grouped
>> into cgroups. Each subdirectory in the cgroupfs mountpoint contains
>> -cpu.pressure, memory.pressure, and io.pressure files; the format is
>> -the same as the /proc/pressure/ files.
>> +cpu.pressure, memory.pressure, and io.pressure files; the format of
>> +memory.pressure and io.pressure is the same as the /proc/pressure/ files.
>> +
>> +But the format of cpu.pressure 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
>
> It's the format of cpu.pressure, except when it's
> /sys/fs/cgroup/cpu.pressure... I think this is getting maybe a tad too
> difficult to write parsers for. Plus, we added the line over a year
> ago so we might break somebody by removing it again.
>
> How about reporting zeroes at the system level?
Ok, it's really better for userspace parsers, will change to this way
and send later.
Thanks.
>
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index e14358178849..86824de404bc 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -1062,14 +1062,17 @@ int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res)
> mutex_unlock(&group->avgs_lock);
>
> for (full = 0; full < 2; full++) {
> - unsigned long avg[3];
> - u64 total;
> + unsigned long avg[3] = { 0, };
> + u64 total = 0;
> int w;
>
> - for (w = 0; w < 3; w++)
> - avg[w] = group->avg[res * 2 + full][w];
> - total = div_u64(group->total[PSI_AVGS][res * 2 + full],
> - NSEC_PER_USEC);
> + /* CPU FULL is undefined at the system level */
> + if (!(group == &psi_system && res == PSI_CPU && full)) {
> + for (w = 0; w < 3; w++)
> + avg[w] = group->avg[res * 2 + full][w];
> + total = div_u64(group->total[PSI_AVGS][res * 2 + full],
> + NSEC_PER_USEC);
> + }
>
> seq_printf(m, "%s avg10=%lu.%02lu avg60=%lu.%02lu avg300=%lu.%02lu total=%llu\n",
> full ? "full" : "some",
