From: Zachary Amsden <zach@vmware.com>
To: Andi Kleen <ak@suse.de>
Cc: Linus Torvalds <torvalds@osdl.org>,
Benjamin LaHaise <bcrl@kvack.org>,
Chuck Ebbert <76306.1226@compuserve.com>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [rfc patch] i386: don't save eflags on task switch
Date: Sun, 05 Nov 2006 00:01:57 -0800 [thread overview]
Message-ID: <454D9A75.7010204@vmware.com> (raw)
In-Reply-To: <200611050641.14724.ak@suse.de>
Andi Kleen wrote:
>> For me, when compiled with -O2, it results in
>>
>> 84
>> 88
>> 132
>>
>> which basically says: a "rdtsc->rdtsc" is 84 cycles, putting a "pushfl" in
>> between is another _4_ cycles, and putting a "popfl" in between is about
>> another 48 cycles.
>>
>
> This means we should definitely change restore_flags() to only STI,
> never popf
>
sti is expensive as well; iirc just as expensive on most processors as
popf, although I don't have hard numbers to back this up on hand. An
_unlikely_ jcc + popf? is better than a sti, for sure, but a likely
jcc+popf could cost more than a jcc+sti, depending on model.
Zach
next prev parent reply other threads:[~2006-11-05 8:01 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-11-04 6:56 [rfc patch] i386: don't save eflags on task switch Chuck Ebbert
2006-11-04 19:09 ` Zachary Amsden
2006-11-04 19:35 ` Linus Torvalds
2006-11-05 3:55 ` Benjamin LaHaise
2006-11-05 4:13 ` Linus Torvalds
2006-11-05 5:41 ` Andi Kleen
2006-11-05 8:01 ` Zachary Amsden [this message]
2006-11-05 17:01 ` Andi Kleen
2006-11-05 17:26 ` Linus Torvalds
2006-11-05 17:34 ` Arjan van de Ven
2006-11-05 17:51 ` Linus Torvalds
2006-11-05 22:48 ` Zachary Amsden
2006-11-05 18:52 ` Andi Kleen
2006-11-05 16:12 ` Linus Torvalds
2006-11-05 16:54 ` Andi Kleen
2006-11-05 17:20 ` Linus Torvalds
2006-11-05 4:17 ` Zachary Amsden
2006-11-05 20:10 ` H. Peter Anvin
-- strict thread matches above, loose matches on Subject: below --
2006-11-04 0:00 Chuck Ebbert
2006-11-04 0:46 ` Linus Torvalds
2006-11-04 1:36 ` Andi Kleen
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