linux-kernel - Re: [Patch V3 0/3] Enable irqs when waiting for rwlocks

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Message-Id: <20081202161311.ae3376cb.akpm@linux-foundation.org>
Date:	Tue, 2 Dec 2008 16:13:11 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	holt@....com
Cc:	linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org,
	ptesarik@...e.cz, tee@....com, holt@....com, peterz@...radead.org,
	mingo@...e.hu, linux-arch@...r.kernel.org
Subject: Re: [Patch V3 0/3] Enable irqs when waiting for rwlocks

On Tue, 04 Nov 2008 06:24:05 -0600
holt@....com wrote:

> New in V3:
>  * Handle rearrangement of some arch's include/asm directories.
> 
> New in V2:
>  * get rid of ugly #ifdef's in kernel/spinlock.h
>  * convert __raw_{read|write}_lock_flags to an inline func
> 
> SGI has observed that on large systems, interrupts are not serviced for
> a long period of time when waiting for a rwlock. The following patch
> series re-enables irqs while waiting for the lock, resembling the code
> which is already there for spinlocks.
> 
> I only made the ia64 version, because the patch adds some overhead to
> the fast path. I assume there is currently no demand to have this for
> other architectures, because the systems are not so large. Of course,
> the possibility to implement raw_{read|write}_lock_flags for any
> architecture is still there.
> 

The patches seem reasonable.  I queued all three with the intention of
merging #1 and #2 into 2.6.29.  At that stage, architectures can decide
whether or not they want to do this.  I shall then spam Tony with #3 so
you can duke it out with him.

It's a bit regrettable to have different architectures behaving in
different ways.  It would be interesting to toss an x86_64
implementation into the grinder, see if it causes any problems, see if
it produces any tangible benefits.  Then other architectures might
follow.  Or not, depending on the results ;)

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