On Mon, Mar 14, 2016 at 09:51:50AM +0100, Heiko Carstens wrote:
> On Fri, Mar 11, 2016 at 11:52:38AM +0100, Anna-Maria Gleixner wrote:
> > The cpumf_pmu_notfier() hotplug callback lacks handling of the
> > CPU_DOWN_FAILED case. That means, if CPU_DOWN_PREPARE failes, the PMC
> > of the CPU is not setup again. Furthermore the CPU_ONLINE_FROZEN case
> > will never be processed because of masking the switch expression with
> > CPU_TASKS_FROZEN.
> >
> > Add handling for CPU_DOWN_FAILED transition to setup the PMC of the
> > CPU. Remove CPU_ONLINE_FROZEN case.
> >
> > Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
> > Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
> > Cc: linux-s390@xxxxxxxxxxxxxxx
> > Signed-off-by: Anna-Maria Gleixner <anna-maria@xxxxxxxxxxxxx>
> > ---
> > arch/s390/kernel/perf_cpum_sf.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > --- a/arch/s390/kernel/perf_cpum_sf.c
> > +++ b/arch/s390/kernel/perf_cpum_sf.c
> > @@ -1518,7 +1518,7 @@ static int cpumf_pmu_notifier(struct not
> >
> > switch (action & ~CPU_TASKS_FROZEN) {
> > case CPU_ONLINE:
> > - case CPU_ONLINE_FROZEN:
> > + case CPU_DOWN_FAILED:
The change looks ok for me.
Acked-by: Hendrik Brueckner <brueckner@xxxxxxxxxxxxxxxxxx>
> > flags = PMC_INIT;
> > smp_call_function_single(cpu, setup_pmc_cpu, &flags, 1);
> > break;
>
> This is a bit odd, but independent from your patch: setup_pmc_cpu() will
> only deallocate buffers but not allocate them.
That's right. Allocation is done when an perf event is about to be scheduled
on a CPU.
>
> Looking at the code a bit further this seems to imply that sampling will
> not work on cpus that were added later.
That might be a problem for task-based perf events. I will have a closer
look into that issue.
Many thanks.
Kind regards,
Hendrik
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