On Fri, May 22, 2015 at 01:21:46PM +0200, Peter Zijlstra wrote:
> @@ -821,8 +828,24 @@ int x86_schedule_events(struct cpu_hw_ev
>
> /* slow path */
> if (i != n) {
> + int gpmax = x86_pmu.num_counters / 2;
> +
> + /*
> + * Do not allow scheduling of more than half the available
> + * generic counters.
> + *
> + * This helps avoid counter starvation of sibling thread by
> + * ensuring at most half the counters cannot be in exclusive
> + * mode. There is no designated counters for the limits. Any
> + * N/2 counters can be used. This helps with events with
> + * specific counter constraints.
> + */
> + if (is_ht_workaround_enabled() && !cpuc->is_fake &&
> + READ_ONCE(cpuc->excl_cntrs->exclusive_present))
> + gpmax /= 2;
> +
> unsched = perf_assign_events(cpuc->event_constraint, n, wmin,
> - wmax, assign);
> + wmax, gpmax, assign);
> }
>
Hmm, I divide by 2 twice.. no wonder it doesn't quite work as expected.
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