linux-kernel - Re: [RFC PATCH 04/21] x86/hweight: Add stack frame dependency for __arch

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Message-ID: <20150722044531.GC6345@nazgul.tnic>
Date:	Wed, 22 Jul 2015 06:45:31 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Michal Marek <mmarek@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Pedro Alves <palves@...hat.com>, live-patching@...r.kernel.org,
	X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC PATCH 04/21] x86/hweight: Add stack frame dependency for
 __arch_hweight*()

On Tue, Jul 21, 2015 at 09:39:23PM -0700, Andy Lutomirski wrote:
> So your shiny perf profile shows cumulative time in whatever called
> them.  Sure, this is arguably silly if we're stuck with frame
> pointers.

You can count 20ish cycles tops for any one of them.

At least that was from the last time when comparing POPCNT perf to the
__sw_hweight* ones. IOW, POPCNT didn't show any improvement vs those sw
versions.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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