From: Matt Sealey <matt@genesi-usa•com>
To: Segher Boessenkool <segher@kernel•crashing.org>
Cc: sfr@canb•auug.org.au, paulus@samba•org, linuxppc-dev@ozlabs•org
Subject: Re: [POWERPC] convert string i/o operations to C
Date: Tue, 19 Sep 2006 21:20:36 +0200 [thread overview]
Message-ID: <45104304.3000205@genesi-usa.com> (raw)
In-Reply-To: <9E674786-9AF3-4322-B642-7BAA58462B74@kernel.crashing.org>
Segher Boessenkool wrote:
>> 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
>
> lwsync (sync 1) doesn't (architecturally) do anything to order MMIO
> accesses, so you're misunderstanding something.
See below :D
>> (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?
>
> No-ops don't matter for performance, compared to the cost of the I/O
> itself. It would help to avoid heavier-than-necessary synchronisation
> instructions if not needed on some certain CPU (or on non-SMP kernels,
> etc.)
But it couldn't hurt, right? There has to be an application note per-CPU
on the correct sequence of operations for such an access (I seem to have
collected a directory full for firmware development), it seems a little
odd to pick and choose one instruction over another for one thing, and
then say you need to do it to support the 601 of all things, and run
this code against the G3/G4/G5 which perhaps doesn't care or is more
intelligent about it (or is guaranteed to have a more intelligent host
bridge at least).
Maybe I'm talking crap, please say so :D
--
Matt Sealey <matt@genesi-usa•com>
Genesi, Manager, Developer Relations
next prev parent reply other threads:[~2006-09-19 19:20 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 [this message]
2006-09-19 19:47 ` Segher Boessenkool
2006-09-19 23:17 ` Benjamin Herrenschmidt
2006-09-19 23:14 ` Benjamin Herrenschmidt
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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