linux-kernel - Re: [PATCH 207/208] x86/fpu: Add FPU performance measurement subsystem

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Date:	Tue, 5 May 2015 21:22:25 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Dave Hansen <dave.hansen@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Andy Lutomirski <luto@...capital.net>,
	Fenghua Yu <fenghua.yu@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 207/208] x86/fpu: Add FPU performance measurement
 subsystem

On Tue, May 05, 2015 at 12:15:00PM -0700, Dave Hansen wrote:
> On 05/05/2015 10:58 AM, Ingo Molnar wrote:
> >   x86/fpu: Cost of: XSAVE                       insn          :   104 cycles
> >   x86/fpu: Cost of: XRSTOR                      insn          :    80 cycles
> 
> Isn't there going to be pretty huge variability here depending on how
> much state you are xsave/xrstor'ing and if the init/modified
> optimizations are in play?

If this is a module, one could modprobe/rmmod it multiple times for
an average. But yeah, it would depend in the end on what the system
does/has been doing in the recent past and thus how much state has been
"accumulated".

-- 
Regards/Gruss,
    Boris.

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