linux-kernel - Re: [PATCH 11/11] perf/x86/intel: Enable conflicting event scheduling for CQM

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Date:	Thu, 8 Jan 2015 12:51:17 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	Kanaka Juvva <kanaka.d.juvva@...el.com>,
	Matt Fleming <matt.fleming@...el.com>
Subject: Re: [PATCH 11/11] perf/x86/intel: Enable conflicting event
 scheduling for CQM

On Fri, Nov 14, 2014 at 09:15:12PM +0000, Matt Fleming wrote:
> +/*
> + * Deallocate the RMIDs from any events that conflict with @event, and
> + * place them on the back of the group list.
> + */
> +static void intel_cqm_sched_out_events(struct perf_event *event)
> +{
> +	struct perf_event *group, *g;
> +	unsigned int rmid;
>  
> +	lockdep_assert_held(&cache_mutex);
> +
> +	list_for_each_entry_safe(group, g, &cache_groups, hw.cqm_groups_entry) {
> +		if (group == event)
> +			continue;
> +
> +		rmid = group->hw.cqm_rmid;
> +
> +		/*
> +		 * Skip events that don't have a valid RMID.
> +		 */
> +		if (!__rmid_valid(rmid))
> +			continue;
> +
> +		/*
> +		 * No conflict? No problem! Leave the event alone.
> +		 */
> +		if (!__conflict_event(group, event))
> +			continue;
> +
> +		intel_cqm_xchg_rmid(group, INVALID_RMID);
> +		__put_rmid(rmid);
> +
> +		list_move_tail(&group->hw.cqm_groups_entry, &cache_groups);
> +	}
>  }

I'm not sure about that list_move_tail() there, is wrecks the rotation
order and would cause conflicting events to get less than their 'fair'
share I suspect.
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