From: Andi Kleen <ak@suse.de>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: Andrea Arcangeli <andrea@suse.de>,
Brian Gerst <bgerst@didntduck.org>,
"H. Peter Anvin" <hpa@zytor.com>,
ak@suse.de, linux-kernel@vger.kernel.org, jh@suse.cz
Subject: Re: [PATCH] Re: SSE related security hole
Date: Sat, 20 Apr 2002 21:41:14 +0200 [thread overview]
Message-ID: <20020420214114.A11894@wotan.suse.de> (raw)
In-Reply-To: <20020420201205.M1291@dualathlon.random> <Pine.LNX.4.33.0204201221120.11732-100000@penguin.transmeta.com>
> Besides, I seriously doubt it is any faster than what is there already.
>
> Time it, and notice how:
>
> - fninit takes about 200 cycles
> - fxrstor takes about 215 cycles
On what CPU?
I checked the Athlon4 optimization manual and fxrstor is listed as 68/108
cycles (i guess depending on whether there is XMM state or not so 68 cycles
probably apply here) and fninit as 91 cycles. It doesn't list the SSE1
timings, but i guess the instructions don't take more than 3 cycles
(MMX instructions take that long). So Andrea's way should be
91+16*3=139+some cycles for emms (or 107 if sse ops take only a single cycle)
vs 68 or 108. So the fxrstor wins well.
On x86-64 the difference is even bigger because it has 16 XMM registers instead
of 8.
> In short, your "fast" code isn't actually any faster than doing it right.
At least on Athlon it should be slower.
-Andi
next prev parent reply other threads:[~2002-04-20 19:41 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20020418183639.20946.qmail@science.horizon.com.suse.lists.linux.kernel>
[not found] ` <a9ncgs$2s2$1@cesium.transmeta.com.suse.lists.linux.kernel>
2002-04-19 14:06 ` SSE related security hole Andi Kleen
2002-04-19 18:00 ` Doug Ledford
2002-04-19 21:04 ` Andrea Arcangeli
2002-04-19 21:35 ` H. Peter Anvin
2002-04-19 21:42 ` Andi Kleen
2002-04-20 3:23 ` Andrea Arcangeli
2002-04-19 23:12 ` [PATCH] " Brian Gerst
2002-04-19 23:41 ` Linus Torvalds
2002-04-20 0:01 ` H. Peter Anvin
2002-04-20 0:09 ` Linus Torvalds
2002-04-20 0:11 ` Brian Gerst
2002-04-20 0:19 ` H. Peter Anvin
2002-04-20 0:29 ` Linus Torvalds
2002-04-20 0:31 ` Alan Cox
2002-04-20 0:08 ` Brian Gerst
2002-04-20 0:21 ` Linus Torvalds
2002-04-20 4:21 ` Andrea Arcangeli
2002-04-20 4:35 ` Linus Torvalds
2002-04-20 5:07 ` Andrea Arcangeli
2002-04-20 16:27 ` Linus Torvalds
2002-04-20 17:27 ` Andrea Arcangeli
2002-04-20 17:38 ` Linus Torvalds
2002-04-20 18:12 ` Andrea Arcangeli
2002-04-20 19:30 ` Linus Torvalds
2002-04-20 19:41 ` Andi Kleen [this message]
2002-04-20 21:28 ` Andrea Arcangeli
2002-04-20 22:43 ` H. Peter Anvin
2002-04-21 2:09 ` Andrea Arcangeli
2002-04-20 23:23 ` Linus Torvalds
2002-04-21 2:08 ` Andrea Arcangeli
2002-04-20 23:13 ` Linus Torvalds
2002-04-23 19:21 ` Linus Torvalds
2002-04-23 20:05 ` H. Peter Anvin
2002-04-24 0:32 ` Andrea Arcangeli
2002-04-24 2:10 ` Linus Torvalds
2002-04-26 9:13 ` Pavel Machek
2002-04-26 11:55 ` Andrea Arcangeli
2002-04-19 22:18 ` Jan Hubicka
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