From: Arnd Bergmann <arnd@arndb.de>
To: linuxppc-dev@ozlabs.org
Cc: Paul Mackerras <paulus@samba.org>
Subject: Re: [RFC 2/3] PowerPC: lazy altivec enabling in kernel
Date: Tue, 24 Apr 2007 10:32:02 +0200 [thread overview]
Message-ID: <200704241032.02856.arnd@arndb.de> (raw)
In-Reply-To: <17965.21687.567012.175024@cargo.ozlabs.ibm.com>
On Tuesday 24 April 2007, Paul Mackerras wrote:
> It would be better to put a test and conditional branch in
> giveup_altivec to skip the mtmsrd if MSR_VEC is already set. =A0That
> would avoid adding the overhead of the trap in the case when MSR_VEC
> isn't already set, besides being much less code.
When I discussed this with Sebastian, my assumption was that even
the mfmsr is rather expensive by itself, but I may have interpreted
the profile data incorrectly.
Do you think it's safe to assume that by skipping mtmsr we can avoid
the bulk of the overhead on most CPUs?
Arnd <><
next prev parent reply other threads:[~2007-04-24 8:32 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-04-17 11:52 [RFC 0/3] Experiments with AES-AltiVec, part 2 Sebastian Siewior
2007-04-17 11:52 ` [RFC 1/3] cryptoapi: AES with AltiVec support Sebastian Siewior
2007-04-17 11:52 ` [RFC 2/3] PowerPC: lazy altivec enabling in kernel Sebastian Siewior
2007-04-24 0:52 ` Paul Mackerras
2007-04-24 8:32 ` Arnd Bergmann [this message]
2007-04-17 11:52 ` [RFC 3/3] cryptoapi: speed test Sebastian Siewior
-- strict thread matches above, loose matches on Subject: below --
2007-04-11 16:49 [RFC 0/3] Experiments with AES-AltiVec Sebastian Siewior
2007-04-11 16:49 ` [RFC 2/3] PowerPC: lazy altivec enabling in kernel Sebastian Siewior
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