linux-kernel - Re: [PATCH V4 04/10] x86, perf: Add conditional branch filtering support

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Date:	Fri, 6 Dec 2013 08:46:43 -0800
From:	Andi Kleen <ak@...ux.intel.com>
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,
	sukadev@...ux.vnet.ibm.com, eranian@...gle.com,
	acme@...stprotocols.net, mingo@...nel.org
Subject: Re: [PATCH V4 04/10] x86, perf: Add conditional branch filtering
 support

On Wed, Dec 04, 2013 at 04:02:36PM +0530, Anshuman Khandual wrote:
> This patch adds conditional branch filtering support,
> enabling it for PERF_SAMPLE_BRANCH_COND in perf branch
> stack sampling framework by utilizing an available
> software filter X86_BR_JCC.

Newer Intel CPUs a hardware filter too for "not a conditional
branch".  I can look at implementing that.

The software option seems fine for now.

-Andi


> 
> Signed-off-by: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
> Reviewed-by: Stephane Eranian <eranian@...gle.com>
> ---
>  arch/x86/kernel/cpu/perf_event_intel_lbr.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> index d82d155..9dd2459 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> @@ -384,6 +384,9 @@ static void intel_pmu_setup_sw_lbr_filter(struct perf_event *event)
>  	if (br_type & PERF_SAMPLE_BRANCH_NO_TX)
>  		mask |= X86_BR_NO_TX;
>  
> +	if (br_type & PERF_SAMPLE_BRANCH_COND)
> +		mask |= X86_BR_JCC;
> +
>  	/*
>  	 * stash actual user request into reg, it may
>  	 * be used by fixup code for some CPU
> @@ -678,6 +681,7 @@ static const int nhm_lbr_sel_map[PERF_SAMPLE_BRANCH_MAX] = {
>  	 * NHM/WSM erratum: must include IND_JMP to capture IND_CALL
>  	 */
>  	[PERF_SAMPLE_BRANCH_IND_CALL] = LBR_IND_CALL | LBR_IND_JMP,
> +	[PERF_SAMPLE_BRANCH_COND]     = LBR_JCC,
>  };
>  
>  static const int snb_lbr_sel_map[PERF_SAMPLE_BRANCH_MAX] = {
> @@ -689,6 +693,7 @@ static const int snb_lbr_sel_map[PERF_SAMPLE_BRANCH_MAX] = {
>  	[PERF_SAMPLE_BRANCH_ANY_CALL]	= LBR_REL_CALL | LBR_IND_CALL
>  					| LBR_FAR,
>  	[PERF_SAMPLE_BRANCH_IND_CALL]	= LBR_IND_CALL,
> +	[PERF_SAMPLE_BRANCH_COND]       = LBR_JCC,
>  };
>  
>  /* core */
> -- 
> 1.7.11.7
> 

-- 
ak@...ux.intel.com -- Speaking for myself only
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