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From: Ingo Molnar <mingo@kernel.org>
To: Eric Biggers <ebiggers3@gmail.com>
Cc: linux-crypto@vger.kernel.org,
	Herbert Xu <herbert@gondor.apana.org.au>,
	"David S . Miller" <davem@davemloft.net>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Jussi Kivilinna <jussi.kivilinna@iki.fi>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	syzkaller-bugs@googlegroups.com,
	Eric Biggers <ebiggers@google.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH] crypto: x86/twofish-3way - Fix %rbp usage
Date: Tue, 19 Dec 2017 08:54:43 +0100	[thread overview]
Message-ID: <20171219075443.tdpt2l72eelhpi7j@gmail.com> (raw)
In-Reply-To: <20171219004026.170565-1-ebiggers3@gmail.com>


* Eric Biggers <ebiggers3@gmail.com> wrote:

> There may be a small overhead caused by replacing 'xchg REG, REG' with
> the needed sequence 'mov MEM, REG; mov REG, MEM; mov REG, REG' once per
> round.  But, counterintuitively, when I tested "ctr-twofish-3way" on a
> Haswell processor, the new version was actually about 2% faster.
> (Perhaps 'xchg' is not as well optimized as plain moves.)

XCHG has implicit LOCK semantics on all x86 CPUs, so that's not a surprising 
result I think.

Thanks,

	Ingo

  reply	other threads:[~2017-12-19  7:54 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-28 18:36 WARNING: kernel stack regs has bad 'bp' value (2) syzbot
2017-11-30  9:17 ` Eric Biggers
2017-12-27 18:29   ` Dmitry Vyukov
2017-12-28  7:30     ` Dmitry Vyukov
2017-12-19  0:40 ` [PATCH] crypto: x86/twofish-3way - Fix %rbp usage Eric Biggers
2017-12-19  7:54   ` Ingo Molnar [this message]
2017-12-19  8:04     ` Juergen Gross
2017-12-19 14:37       ` David Laight
2017-12-19 17:35     ` Ingo Molnar
2017-12-19 22:37   ` Josh Poimboeuf
2017-12-28  7:02   ` Herbert Xu

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