Messages in this thread Patch in this message | | | From | Valentin Schneider <> | Subject | Re: [PATCH] sched/debug: Fix requested task uclamp values shown in procfs | Date | Sun, 10 May 2020 17:16:28 +0100 |
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On 10/05/20 13:56, Pavankumar Kondeti wrote: > The intention of commit 96e74ebf8d59 ("sched/debug: Add task uclamp > values to SCHED_DEBUG procfs") was to print requested and effective > task uclamp values. The requested values printed are read from p->uclamp, > which holds the last effective values. Fix this by printing the values > from p->uclamp_req. > > Fixes: 96e74ebf8d59 ("sched/debug: Add task uclamp values to SCHED_DEBUG procfs") > Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Argh, Qais pointed this out to me ~ a week ago, and I left this in my todo stack. I goofed up, sorry!
As Pavan points out, p->uclamp[foo] is just a cache of uclamp_eff_value(p, foo) from the last time p was enqueued and runnable - what we are interested in is indeed comparing this with the *requested* value.
I wanted to send an example along with a patch, I guess that's the kick I needed!
My setup is a busy loop, its per-task clamps are set to (256, 768) via sched_setattr(), and it's shoved in a cpu cgroup with uclamp settings of (50%, 50%)
On the current master (e99332e7b4cd ("gcc-10: mark more functions __init to avoid section mismatch warnings")), this gives me:
$ uclamp-get $PID # via sched_getattr() uclamp.min=256 uclamp.max=768
$ cat /proc/$PID/sched | grep uclamp uclamp.min : 256 uclamp.max : 512 effective uclamp.min : 256 effective uclamp.max : 512
With Pavan's patch, I get:
$ uclamp-get $PID # via sched_getattr() uclamp.min=256 uclamp.max=768
$ cat /proc/$PID/sched | grep uclamp uclamp.min : 256 uclamp.max : 768 effective uclamp.min : 256 effective uclamp.max : 512
Minor print nit below, otherwise: Tested-and-reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Peter/Ingo, any chance this can go to sched/urgent? I know it's a debug interface, but I'd rather have it land in a shape that makes sense. Again, apologies for the goof.
> --- > kernel/sched/debug.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c > index a562df5..239970b 100644 > --- a/kernel/sched/debug.c > +++ b/kernel/sched/debug.c > @@ -948,8 +948,8 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns, > P(se.avg.util_est.enqueued); > #endif > #ifdef CONFIG_UCLAMP_TASK > - __PS("uclamp.min", p->uclamp[UCLAMP_MIN].value); > - __PS("uclamp.max", p->uclamp[UCLAMP_MAX].value); > + __PS("uclamp.min", p->uclamp_req[UCLAMP_MIN].value); > + __PS("uclamp.max", p->uclamp_req[UCLAMP_MAX].value);
While we're at it, I'd prepend this with "requested".
> __PS("effective uclamp.min", uclamp_eff_value(p, UCLAMP_MIN)); > __PS("effective uclamp.max", uclamp_eff_value(p, UCLAMP_MAX)); > #endif
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