From: Arjan van de Ven <arjan@infradead.org>
To: Linus Torvalds <torvalds@osdl.org>
Cc: Andrew Morton <akpm@osdl.org>,
Chuck Ebbert <76306.1226@compuserve.com>,
linux-kernel@vger.kernel.org
Subject: Re: [patch 2.6.13-rc3a] i386: inline restore_fpu
Date: Fri, 22 Jul 2005 07:23:32 -0400 [thread overview]
Message-ID: <1122031412.3577.27.camel@localhost.localdomain> (raw)
In-Reply-To: <Pine.LNX.4.58.0507212211400.6074@g5.osdl.org>
> > We do have the `used_math' optimisation in there which attempts to avoid
> > doing the FP save/restore if the app isn't actually using math.
>
> No, it's more than that. There's a per-processor "used_math" flag to
> determine if we need to _initialize_ the FPU, but on context switches we
> always assume the program we're switching to will _not_ use FP, and we
> just set the "fault on FP" flag and do not normally restore FP state.
This shows room for optimization; if an app is consistently faulting to
use FP after a context switch, in principle the kernel could start to
assume that it will in the next timeslice as well.
> On the other hand, I also wouldn't be surprised if glibc (or similar
I doubt glibc is normally, at least most distros don't ship an SSE
enabled glibc, only an "i686" one.
next prev parent reply other threads:[~2005-07-22 11:23 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-07-22 3:06 [patch 2.6.13-rc3a] i386: inline restore_fpu Chuck Ebbert
2005-07-22 3:27 ` Andrew Morton
2005-07-22 5:22 ` Linus Torvalds
2005-07-22 11:23 ` Arjan van de Ven [this message]
2005-07-22 8:14 ` Adrian Bunk
2005-07-22 18:13 ` Linus Torvalds
2005-07-25 19:26 ` Bill Davidsen
2005-07-22 23:19 ` Linus Torvalds
-- strict thread matches above, loose matches on Subject: below --
2005-07-22 9:58 Chuck Ebbert
2005-07-23 7:09 Chuck Ebbert
2005-07-23 17:38 ` Linus Torvalds
2005-07-23 17:46 ` Arjan van de Ven
2005-07-23 18:02 ` Linus Torvalds
2005-07-23 7:09 Chuck Ebbert
2005-07-23 17:33 ` Linus Torvalds
[not found] <200507212309_MC3-1-A534-95EF@compuserve.com.suse.lists.linux.kernel>
[not found] ` <20050722132756.578acca7.akpm@osdl.org.suse.lists.linux.kernel>
2005-07-23 15:35 ` Andi Kleen
2005-07-24 12:56 Kenneth Parrish
2005-07-25 2:34 Kenneth Parrish
2005-07-26 21:23 Chuck Ebbert
2005-07-26 21:23 Chuck Ebbert
2005-07-26 21:47 ` Linus Torvalds
2005-07-27 1:40 linux
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