linux-kernel - Re: [PATCH 2/5] powerpc, perf: Enable conditional branch filter for POWER8

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Message-ID: <20130522075305.GN26912@twins.programming.kicks-ass.net>
Date:	Wed, 22 May 2013 09:53:05 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
	michael@...erman.id.au, mikey@...ling.org, eranian@...gle.com,
	ak@...ux.intel.com, mingo@...nel.org
Subject: Re: [PATCH 2/5] powerpc, perf: Enable conditional branch filter for
 POWER8

On Wed, May 22, 2013 at 11:52:38AM +0530, Anshuman Khandual wrote:
> Enables conditional branch filter support for POWER8
> utilizing MMCRA register based filter and also invalidates
> a BHRB branch filter combination involving conditional
> branches.
> 
> Signed-off-by: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
> ---
>  arch/powerpc/perf/power8-pmu.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/arch/powerpc/perf/power8-pmu.c b/arch/powerpc/perf/power8-pmu.c
> index 8ed323d..e60b38f 100644
> --- a/arch/powerpc/perf/power8-pmu.c
> +++ b/arch/powerpc/perf/power8-pmu.c
> @@ -548,11 +548,21 @@ static u64 power8_bhrb_filter_map(u64 branch_sample_type)
>  	if (branch_sample_type & PERF_SAMPLE_BRANCH_IND_CALL)
>  		return -1;
>  
> +	/* Invalid branch filter combination - HW does not support */
> +	if ((branch_sample_type & PERF_SAMPLE_BRANCH_ANY_CALL) &&
> +			(branch_sample_type & PERF_SAMPLE_BRANCH_COND))
> +		return -1;
> +
>  	if (branch_sample_type & PERF_SAMPLE_BRANCH_ANY_CALL) {
>  		pmu_bhrb_filter |= POWER8_MMCRA_IFM1;
>  		return pmu_bhrb_filter;
>  	}
>  
> +	if (branch_sample_type & PERF_SAMPLE_BRANCH_COND) {
> +		pmu_bhrb_filter |= POWER8_MMCRA_IFM3;
> +		return pmu_bhrb_filter;
> +	}
> +
>  	/* Every thing else is unsupported */
>  	return -1;
>  }

So I suppose you've seen what x86 does in this case? ;-) I'm not saying
you _have_ to do the software filter, but I would like the changelog to at
least mention the issue.

In fact, I suppose that should have been in the original patches :/ as
this patch series only adds the conditional branch support. 

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