From: Peter Zijlstra <peterz@infradead.org>
To: Vince Weaver <vincent.weaver@maine.edu>
Cc: LKML <linux-kernel@vger.kernel.org>,
Stephane Eranian <eranian@google.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Jiri Olsa <jolsa@redhat.com>, Ingo Molnar <mingo@redhat.com>,
Paul Mackerras <paulus@samba.org>
Subject: Re: perf: odd event scheduling issue
Date: Wed, 20 May 2015 18:28:11 +0200 [thread overview]
Message-ID: <20150520162811.GN18673@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20150520160802.GL18673@twins.programming.kicks-ass.net>
On Wed, May 20, 2015 at 06:08:02PM +0200, Peter Zijlstra wrote:
> @@ -2062,6 +2081,22 @@ intel_get_excl_constraints(struct cpu_hw_events *cpuc, struct perf_event *event,
> */
>
> /*
> + * Do not allow scheduling of more than max_alloc_cntrs
> + * which is set to 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 not designated counters for the
> + * limits. Any N/2 counters can be used. This helps with
> + * events with specifix counter constraints
> + */
> + if (xl->num_alloc_cntrs++ >= xl->max_alloc_cntrs) {
> + /* wipe the GP counters */
> + cx->idxmsk64 &= ~((1ULL << INTEL_PMC_IDX_FIXED) - 1);
> + goto done;
> + }
> +
> + /*
> * Modify static constraint with current dynamic
> * state of thread
> *
While this improves things, its still sub optimal because we should only
increase num_alloc_cntrs when we actually allocate a GP register, but we
do that at commit time and that callback is too late to back out / retry.
So ideally we'd move the callback into scheduling code, but that means
we also have to move the xlo array into the sched_state etc.
[ which brings me to the whole xl vs xlo thing, I think we done that the
wrong way around. It would be more natural to account to xl and create
constraints based on xlo. ]
Secondly, we should only enforce this limit if and when there are
exclusive events on the system I suppose.
I have some ideas on how to go do this, but I need a break..
next prev parent reply other threads:[~2015-05-20 16:28 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-20 3:07 perf: odd event scheduling issue Vince Weaver
2015-05-20 7:00 ` Peter Zijlstra
2015-05-20 7:11 ` Jiri Olsa
2015-05-20 9:28 ` Peter Zijlstra
2015-05-20 13:52 ` Peter Zijlstra
2015-05-20 15:25 ` Peter Zijlstra
2015-05-20 16:08 ` Peter Zijlstra
2015-05-20 16:28 ` Peter Zijlstra [this message]
2015-05-20 23:10 ` Andi Kleen
2015-05-21 12:04 ` Stephane Eranian
2015-05-20 16:25 ` Jiri Olsa
2015-05-21 12:05 ` Stephane Eranian
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