From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Matt Sealey <matt@genesi-usa.com>
Cc: sfr@canb.auug.org.au, paulus@samba.org, linuxppc-dev@ozlabs.org
Subject: Re: [POWERPC] convert string i/o operations to C
Date: Wed, 20 Sep 2006 09:14:36 +1000 [thread overview]
Message-ID: <1158707676.6002.174.camel@localhost.localdomain> (raw)
In-Reply-To: <45103DF0.9050409@genesi-usa.com>
On Tue, 2006-09-19 at 20:58 +0200, Matt Sealey wrote:
> Shouldn't this stuff be optimized out depending on what processor you're
> ACTUALLY running?
>
> For a generic "powerpc" kernel it can be understood, but when you
> consider that on 970/POWER4 and above they use lwsync instead of sync
> (google for them and see the mailing list posts :), just to breathe back
> some performance in spinlocks and so on, surely this can be rejigged so
> that processors don't do more work than necessary..? Even a noop takes
> time doesn't it?
The architecture is precise enough there. It should be twi,isync. The
goal of the isync is to make sure no subsequent instruction can execute
until the previous conditional branch has been fully resolved, which
implies loading the dependent data. An isync is the only instruction in
this specific case that is guaranteed to provide what we need by the
architecture.
Ben
next prev parent reply other threads:[~2006-09-19 23:14 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-09-19 12:23 [POWERPC] convert string i/o operations to C Stephen Rothwell
2006-09-19 12:42 ` David Howells
2006-09-19 23:07 ` Stephen Rothwell
2006-09-19 18:29 ` Linas Vepstas
2006-09-19 18:52 ` Kim Phillips
2006-09-19 18:58 ` Matt Sealey
2006-09-19 19:10 ` Segher Boessenkool
2006-09-19 19:20 ` Matt Sealey
2006-09-19 19:47 ` Segher Boessenkool
2006-09-19 23:17 ` Benjamin Herrenschmidt
2006-09-19 23:14 ` Benjamin Herrenschmidt [this message]
2006-09-19 19:04 ` Linas Vepstas
2006-09-19 19:06 ` Segher Boessenkool
2006-09-19 23:12 ` Benjamin Herrenschmidt
2006-09-20 0:03 ` Segher Boessenkool
2006-09-20 0:08 ` Benjamin Herrenschmidt
2006-09-20 0:29 ` Segher Boessenkool
2006-09-20 3:35 ` Stephen Rothwell
2006-09-20 4:38 ` Michael Ellerman
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