linux-kernel - Re: [tip:perf/core] perf/x86/intel: Clean-up/reduce PEBS code

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Message-ID: <87mwng53ki.fsf@tassilo.jf.intel.com>
Date:	Fri, 13 Sep 2013 23:18:21 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	mingo@...nel.org
Cc:	hpa@...or.com, linux-kernel@...r.kernel.org, peterz@...radead.org,
	tglx@...utronix.de, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/core] perf/x86/intel: Clean-up/reduce PEBS code

tip-bot for Peter Zijlstra <tipbot@...or.com> writes:
> +
> +	at  = (struct pebs_record_nhm *)(unsigned long)ds->pebs_buffer_base;
> +	top = (struct pebs_record_nhm *)(unsigned long)ds->pebs_index;
>  
>  	ds->pebs_index = ds->pebs_buffer_base;
>  
> +	n = (top - at) / x86_pmu.pebs_record_size;


This adds a full slow division to the PEBS hot path.

Does not seem like a improvement to me.

-Andi

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