From: Segher Boessenkool <segher@kernel.crashing.org>
To: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Cc: Arnd Bergmann <arnd@arndb.de>, Akinobu Mita <mita@fixstars.com>,
linuxppc-dev list <linuxppc-dev@ozlabs.org>,
Paul Mackerras <paulus@samba.org>,
cbe-oss-dev@ozlabs.org
Subject: Re: [PATCH] force -mno-string option on cell
Date: Mon, 26 Mar 2007 14:33:07 +0200 [thread overview]
Message-ID: <2900f15414598ecb5ebb6845f6defe86@kernel.crashing.org> (raw)
In-Reply-To: <Pine.LNX.4.62.0703261054180.8896@pademelon.sonytel.be>
>>> strings instructions suck, get away with it.
>>
>> No they don't.
>>
>> End of this particular subthread I suppose, heh.
>
> Really? `They suck!' 'They don't!'...
>
> Ben: Why do they suck?
> Segher: Why don't they suck?
On most CPUs, they perform just fine, microcoded or not,
in most circumstances (hint: the bottleneck is not at the
decode stage). They can actually help because of improved
code density.
For CPUs where they do suck, GCC knows (or should know)
preferably not to generate them. Like on CBE, where lswi
causes a lovely 11-cycle bubble. But guess what, many
more insns do so -- and we're not going to unconditionally
add a compiler flag to every kernel build that prevents
the compiler from generating "andi." insns I hope :-)
Segher
prev parent reply other threads:[~2007-03-26 12:33 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-03-22 6:23 [PATCH] powerpc: Always use -mno-string Benjamin Herrenschmidt
2007-03-22 12:06 ` Segher Boessenkool
2007-03-23 12:06 ` [PATCH] force -mno-string option on cell Akinobu Mita
2007-03-23 12:56 ` Segher Boessenkool
2007-03-23 19:38 ` Benjamin Herrenschmidt
2007-03-24 0:02 ` Segher Boessenkool
2007-03-23 20:46 ` [Cbe-oss-dev] " Arnd Bergmann
2007-03-26 12:00 ` Segher Boessenkool
2007-03-24 3:02 ` Paul Mackerras
2007-03-24 14:46 ` Segher Boessenkool
2007-03-23 13:37 ` Kumar Gala
2007-03-23 16:35 ` Segher Boessenkool
2007-03-23 19:46 ` Benjamin Herrenschmidt
2007-03-24 0:04 ` Segher Boessenkool
2007-03-26 8:54 ` Geert Uytterhoeven
2007-03-26 12:33 ` Segher Boessenkool [this message]
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