Re: [tip:perf/core] perf: Rework the PMU methods

Michael Cree
2010-09-11T08:16:27Z

On 10/09/10 07:50, tip-bot for Peter Zijlstra wrote:
> Commit-ID: a4eaf7f14675cb512d69f0c928055e73d0c6d252
> Gitweb: http://git.kernel.org/tip/a4eaf7f14675cb512d69f0c928055e73d0c6d252
> Author: Peter Zijlstra<a.p.zijlstra@chello.nl>
> AuthorDate: Wed, 16 Jun 2010 14:37:10 +0200
> Committer: Ingo Molnar<mingo@elte.hu>
> CommitDate: Thu, 9 Sep 2010 20:46:30 +0200
>
> perf: Rework the PMU methods
>
> Replace pmu::{enable,disable,start,stop,unthrottle} with
> pmu::{add,del,start,stop}, all of which take a flags argument.

Regarding the new function alpha_pmu_stop() in
arch/alpha/kernel/perf_event.c:

> -static void alpha_pmu_unthrottle(struct perf_event *event)
> +static void alpha_pmu_stop(struct perf_event *event, int flags)
> {
> struct hw_perf_event *hwc =&event->hw;
> struct cpu_hw_events *cpuc =&__get_cpu_var(cpu_hw_events);
>
> + if (!(hwc->state& PERF_HES_STOPPED)) {
> + cpuc->idx_mask&= !(1UL<<hwc->idx);
^
Presumably ones complement (rather than logical not) is meant.

> + hwc->state |= PERF_HES_STOPPED;
> + }
> +
> + if ((flags& PERF_EF_UPDATE)&& !(hwc->state& PERF_HES_UPTODATE)) {
> + alpha_perf_event_update(event, hwc, hwc->idx, 0);
> + hwc->state |= PERF_HES_UPTODATE;
> + }
> +
> + if (cpuc->enabled)
> + wrperfmon(PERFMON_CMD_ENABLE, (1UL<<hwc->idx));

By the name of the function (alpha_pmu_stop) I assume that the intent is
to stop the specific PMC here. The above fails to do that. When
wrperfmon() is used with PERFMON_CMD_ENABLE it enables the PMCs with set
bits in the second argument. It does not stop the others. To do that
wrperfmon() must be called with PERFMON_CMD_DISABLE and the
corresponding PMC bits set to disable the PMC.

Cheers
Michael.