linux-kernel - Re: [RFC][PATCH 1/7] perf/x86/intel: Rework the large PEBS setup code

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Message-ID: <20160708163616.GA2392@krava>
Date:	Fri, 8 Jul 2016 18:36:16 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, acme@...nel.org, linux-kernel@...r.kernel.org,
	andi@...stfloor.org, eranian@...gle.com, jolsa@...nel.org,
	torvalds@...ux-foundation.org, davidcc@...gle.com,
	alexander.shishkin@...ux.intel.com, namhyung@...nel.org,
	kan.liang@...el.com, khandual@...ux.vnet.ibm.com
Subject: Re: [RFC][PATCH 1/7] perf/x86/intel: Rework the large PEBS setup code

On Fri, Jul 08, 2016 at 03:31:00PM +0200, Peter Zijlstra wrote:

SNIP

>  	/*
> -	 * When the event is constrained enough we can use a larger
> -	 * threshold and run the event with less frequent PMI.
> +	 * Use auto-reload if possible to save a MSR write in the PMI.
> +	 * This must be done in pmu::start(), because PERF_EVENT_IOC_PERIOD.
>  	 */
> -	if (hwc->flags & PERF_X86_EVENT_FREERUNNING) {
> -		threshold = ds->pebs_absolute_maximum -
> -			x86_pmu.max_pebs_events * x86_pmu.pebs_record_size;
> -
> -		if (first_pebs)
> -			perf_sched_cb_inc(event->ctx->pmu);
> -	} else {
> -		threshold = ds->pebs_buffer_base + x86_pmu.pebs_record_size;
> -
> -		/*
> -		 * If not all events can use larger buffer,
> -		 * roll back to threshold = 1
> -		 */
> -		if (!first_pebs &&
> -		    (ds->pebs_interrupt_threshold > threshold))
> -			perf_sched_cb_dec(event->ctx->pmu);
> -	}

hum, the original code switched back the perf_sched_cb,
in case !feerunning event was detected.. I dont see it
in the new code.. just the threshold update

jirka