linux-kernel - Re: [PATCH] Fix x86_64 _spin_lock

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Message-Id: <20060823214831.aa687ebe.akpm@osdl.org>
Date:	Wed, 23 Aug 2006 21:48:31 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Edward Falk <efalk@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix x86_64 _spin_lock_irqsave()

On Thu, 24 Aug 2006 13:10:09 +1000
Nick Piggin <nickpiggin@...oo.com.au> wrote:

> Edward Falk wrote:
> > Add spin_lock_string_flags and _raw_spin_lock_flags() to 
> > asm-x86_64/spinlock.h so that _spin_lock_irqsave() has the same 
> > semantics on x86_64 as it does on i386 and does *not* have interrupts 
> > disabled while it is waiting for the lock.
> > 
> > This fix is courtesy of Michael Davidson
> 
> So, what's the bug? You shouldn't rely on these semantics anyway
> because you should never expect to wait for a spinlock for so long
> (and it may be the case that irqs can't be enabled anyway).
> 
> BTW. you should be cc'ing Andi Kleen (x86+/-64 maintainer) on
> this type of stuff.
> 
> No comments on the merits of adding this feature. I suppose parity
> with i386 is a good thing, though.
> 

We put this into x86 ages ago and Andi ducked the x86_64 patch at the time.

I don't recall any reports about the x86 patch (Zwane?) improving or
worsening anything.  I guess there are some theoretical interrupt latency
benefits.

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