linux-kernel - Re: [PATCH] perf/x86/amd/ibs: Fix sample bias for dispatched micro-ops

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Message-ID: <20190828080259.GM2332@hirez.programming.kicks-ass.net>
Date:   Wed, 28 Aug 2019 10:02:59 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kim Phillips <kim.phillips@....com>
Cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        Stephane Eranian <eranian@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] perf/x86/amd/ibs: Fix sample bias for dispatched
 micro-ops

On Mon, Aug 26, 2019 at 02:57:30PM -0500, Kim Phillips wrote:

> diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
> index 62f317c9113a..f2625b4a5a8b 100644
> --- a/arch/x86/events/amd/ibs.c
> +++ b/arch/x86/events/amd/ibs.c
> @@ -663,8 +663,15 @@ static int perf_ibs_handle_irq(struct perf_ibs *perf_ibs, struct pt_regs *iregs)
>  out:
>  	if (throttle)
>  		perf_ibs_stop(event, 0);
> -	else
> -		perf_ibs_enable_event(perf_ibs, hwc, period >> 4);
> +	else {

Coding Style requires braces on both legs of a conditional.

> +		period >>= 4;
> +
> +		if ((ibs_caps & IBS_CAPS_RDWROPCNT) &&
> +		    (*config & IBS_OP_CNT_CTL))
> +			period |= *config & IBS_OP_CUR_CNT_RAND;
> +
> +		perf_ibs_enable_event(perf_ibs, hwc, period);
> +	}
>  
>  	perf_event_update_userpage(event);
>  
> diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
> index 1392d5e6e8d6..67d94696a1d6 100644
> --- a/arch/x86/include/asm/perf_event.h
> +++ b/arch/x86/include/asm/perf_event.h
> @@ -259,9 +259,12 @@ struct pebs_lbr {
>  #define IBS_FETCH_CNT		0xFFFF0000ULL
>  #define IBS_FETCH_MAX_CNT	0x0000FFFFULL
>  
> -/* ibs op bits/masks */
> -/* lower 4 bits of the current count are ignored: */
> -#define IBS_OP_CUR_CNT		(0xFFFF0ULL<<32)
> +/* ibs op bits/masks
> + * The lower 7 bits of the current count are random bits
> + * preloaded by hardware and ignored in software
> + */

Malformed comment style.

> +#define IBS_OP_CUR_CNT		(0xFFF80ULL<<32)
> +#define IBS_OP_CUR_CNT_RAND	(0x0007FULL<<32)
>  #define IBS_OP_CNT_CTL		(1ULL<<19)
>  #define IBS_OP_VAL		(1ULL<<18)
>  #define IBS_OP_ENABLE		(1ULL<<17)

Fixed up both issues and applied.

Thanks!