linux-kernel - Re: [PATCH V4 04/16] perf, x86: Basic Haswell LBR call stack support

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Message-ID: <20140702101430.GW6758@twins.programming.kicks-ass.net>
Date:	Wed, 2 Jul 2014 12:14:30 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Yan, Zheng" <zheng.z.yan@...el.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org, acme@...radead.org,
	eranian@...gle.com, andi@...stfloor.org
Subject: Re: [PATCH V4 04/16] perf, x86: Basic Haswell LBR call stack support

On Mon, Jun 30, 2014 at 04:50:41PM +0800, Yan, Zheng wrote:
> @@ -438,8 +451,11 @@ static int intel_pmu_setup_hw_lbr_filter(struct perf_event *event)
>  	reg = &event->hw.branch_reg;
>  	reg->idx = EXTRA_REG_LBR;
>  
> -	/* LBR_SELECT operates in suppress mode so invert mask */
> -	reg->config = ~mask & x86_pmu.lbr_sel_mask;
> +	/*
> +	 * the first 8 bits (LBR_SEL_MASK) in LBR_SELECT operates
> +	 * in suppress mode so invert mask
> +	 */
> +	reg->config = mask ^ x86_pmu.lbr_sel_mask;

Where the comment made sense with the old code; it doesn't really with
the new..

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