Date: Sat, 21 Feb 2015 19:39:52 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>, Oleg Nesterov <oleg@redhat.com>,
        Rik van Riel <riel@redhat.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [RFC PATCH] x86, fpu: Use eagerfpu by default on all CPUs
Message-ID: <20150221183952.GD8406@gmail.com>
References: <b0ba174ea882ed36cf7011e872baf427c23b7e09.1424458621.git.luto@amacapital.net>
 <20150221093150.GA27841@gmail.com>
 <20150221163840.GA32073@pd.tnic>
 <20150221172914.GB32073@pd.tnic>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20150221172914.GB32073@pd.tnic>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1112
Lines: 33


* Borislav Petkov <bp@alien8.de> wrote:

> On Sat, Feb 21, 2015 at 05:38:40PM +0100, Borislav Petkov wrote:
> > My assumption is that libc uses SSE for memcpy and thus the FPU will
> > be used. (I'll trace FPU-specific PMCs later to confirm).
> 
> Ok, so I slapped a trace_printk() at the beginning of fpu_save_init()
> and did a kernel build once with default 3.19 and once with Andy's
> patch. So we end up with this count:
> 
> default: 712000
> eager:   780000
> 
> This would explain the very small difference in the 
> performance counters data from the previous email.

So the workload improved by ~600,000 usecs, and there's 
68,000 less calls, so it saved 8.8 usecs per call. Isn't 
that a bit too high?

I'd sleep a lot better if we had some runtime debug flag to 
be able to do run-to-run comparisons on the same booted up 
kernel, or so.

Thanks,

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/