From: Matt Sealey <matt@genesi-usa•com>
To: Kim Phillips <kim.phillips@freescale•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: Tue, 19 Sep 2006 20:58:56 +0200 [thread overview]
Message-ID: <45103DF0.9050409@genesi-usa.com> (raw)
In-Reply-To: <20060919135259.303706d3.kim.phillips@freescale.com>
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?
--
Matt Sealey <matt@genesi-usa•com>
Genesi, Manager, Developer Relations
Kim Phillips wrote:
> On Tue, 19 Sep 2006 13:29:53 -0500
> linas@austin•ibm.com (Linas Vepstas) wrote:
>
>> What does this twi do? According to my powerpc docs, this would be a
>> no-op. Does this have some magic synchronizing powers on certain
>> implementations? If so, there should be at least a comment card added
>> about why the twi is there. (This special ability of twi might be
>> well-known to some, but still, this is not immediately obvious,
>> and not immedately documented in e.g. the PEM.)
>
> include/asm-p[ower]pc/io.h sheds some light on the matter:
>
> * With the sequence below (twi; isync; nop), we have found that
> * the machine check occurs on one of the three instructions on
> * all PPC implementations tested so far. The twi and isync are
> * needed on the 601 (in fact twi; sync works too), the isync and
> * nop are needed on 604[e|r], and any of twi, sync or isync will
> * work on 603[e], 750, 74xx.
> * The twi creates an explicit data dependency on the returned
> * value which seems to be needed to make the 601 wait for the
> * load to finish.
>
> Kim
> _______________________________________________
> Linuxppc-dev mailing list
> Linuxppc-dev@ozlabs•org
> https://ozlabs.org/mailman/listinfo/linuxppc-dev
next prev parent reply other threads:[~2006-09-19 18:59 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 [this message]
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
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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