From: "George Spelvin" <linux@horizon.com>
To: andi@firstfloor.org, linux@horizon.com
Cc: linux-kernel@vger.kernel.org
Subject: Re: How to measure enable_kernel_fpu overhead?
Date: 4 Jun 2011 21:50:23 -0400 [thread overview]
Message-ID: <20110605015023.9860.qmail@science.horizon.com> (raw)
In-Reply-To: <20110605003118.GP27166@one.firstfloor.org>
> Different CPU models. This years CPUs does this and next years that.
Er, yes, exactly. That's why we have multiple code paths, and
run-time selection of the best. The basic principle is used rather
a lot in the Linux kernel, e.g. the alternative() feature.
To me the closest equivalent is the RAID6 code, which has no less than 12
different versions (5 integer, 4 AltiVec, 1 MMX, 1 SSE1, and 1 SSE2),
and on x86 it benchmarks the 8 different versions at boot time and
chooses the best.
What confuses me is:
> I would suggest KISS.
This suggestion is not quite clear to me; I'm not quite sure what you
think is "simple". Do you mean always use the integer code and ignore
the SSE registers? Or something else?
Could you expand on that remark a little, please?
Thank you!
next prev parent reply other threads:[~2011-06-05 1:50 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-03 17:26 George Spelvin
2011-06-04 20:17 ` Andi Kleen
2011-06-05 0:23 ` George Spelvin
2011-06-05 0:31 ` Andi Kleen
2011-06-05 1:50 ` George Spelvin [this message]
[not found] <BANLkTimyCodUvBUEVUJcb8TALF5x3H3UEQ@mail.gmail.com>
2011-06-05 15:51 ` George Spelvin
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