From: Paul Mackerras <paulus@samba.org>
To: Nick Piggin <npiggin@suse.de>
Cc: Anton Blanchard <anton@samba.org>, linuxppc-dev@ozlabs.org
Subject: Re: [rfc][patch] powerpc: replace isync with lwsync
Date: Mon, 3 Nov 2008 16:32:22 +1100 [thread overview]
Message-ID: <18702.36070.59703.535800@cargo.ozlabs.ibm.com> (raw)
In-Reply-To: <20081101130715.GC32055@wotan.suse.de>
Nick Piggin writes:
> This is an interesting one for me. AFAIKS it is possible to use lwsync for
> a full barrier after a successful ll/sc operation, right? (or stop me here
> if I'm wrong).
An lwsync would order subsequent loads after the lwarx/ldarx, and
subsequent stores after the stcwx./stcdx., which should be good
enough.
> isync followed by a branch I guess does something like puts a bubble
> into the pipeline until the branch retires? So it is probably always
> going to cost some cycles.
I don't know about "retires", but isync is going to stop following
instructions from executing until the outcome of the branch is known.
On machines that don't have lwsync we will still want to use isync
(since the other alternative would be the full heavyweight sync).
Your patch doesn't seem to do that.
Paul.
next prev parent reply other threads:[~2008-11-03 5:32 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-11-01 12:33 [patch] powerpc: smp_wmb lwsync optimisation fix Nick Piggin
2008-11-01 13:05 ` [patch] powerpc: rmp_wmb lwsync optimisation Nick Piggin
2008-11-01 13:07 ` [rfc][patch] powerpc: replace isync with lwsync Nick Piggin
2008-11-03 5:32 ` Paul Mackerras [this message]
2008-11-03 8:31 ` Nick Piggin
2008-11-01 16:47 ` [patch] powerpc: smp_wmb lwsync optimisation fix Kumar Gala
2008-11-02 1:42 ` Nick Piggin
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