linux-kernel - Re: [PATCH V2 0/2] enable irqs when waiting for rwlocks

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Message-ID: <20081103114638.GD8483@sgi.com>
Date:	Mon, 3 Nov 2008 05:46:39 -0600
From:	Robin Holt <holt@....com>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	Petr Tesarik <ptesarik@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>
Subject: Re: [PATCH V2 0/2] enable irqs when waiting for rwlocks

On Fri, Oct 31, 2008 at 01:22:56PM -0700, Luck, Tony wrote:
> > Any comments on my second patch series? Not even an Acked-by? Dislike of
> > the concept? Should I post it again?
> 
> Better response to interrupts is good, but it comes at the
> cost of longer latency acquiring the lock (in the case where
> an interrupt happens while we are waiting for the lock, and
> the lock is freed while we are off executing the interrupt
> handler).
> 
> Any suggestions on how to measure the trade-off here?  Possibly
> it doesn't matter because this may only be significant when
> the lock is heavily contended and you are probably aleady
> hosed in this case.

Just a few years of experiencal evidence.  The equivalent of this patch
has been in the SuSE SLES10 kernel for years and not been detected as
being negative.

Sorry I don't have more detail.  The person at SGI who first detected
this problem has long since left, and actually passed away from an
aneurysm a couple years ago.  The first version of the patch was in our
one-off kernel based on Redhat's 2.4 kernel.  The patch was not pushed
to SuSE and the community for SLES9.  It was in SLES10, but I can not
find our internal tracking tool's record of it (searching is failing me
this morning).  Without that, I have not been able to find why it was
not pushed to the community.

Thanks,
Robin
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