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

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Date:	Thu, 23 Oct 2008 09:12:32 -0500
From:	Robin Holt <holt@....com>
To:	Rick Jones <rick.jones2@...com>
Cc:	Petr Tesarik <ptesarik@...e.cz>, linux-kernel@...r.kernel.org,
	linux-ia64@...r.kernel.org, tee@....com
Subject: Re: [PATCH 0/2] enable irqs when waiting for rwlocks

On Wed, Oct 22, 2008 at 10:31:53AM -0700, Rick Jones wrote:
> Petr Tesarik wrote:
>> Hello,
>>
>> 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.
>
> Perhaps I'm just out in left field, but that (and the similar behaviour  
> for obtaining a spinlock?) feels like treating a symptom rather than a  
> root cause where the root cause would appear to be long lock hold  
> times/contention?

Sometimes lock contention on large systems will take a few seconds to
pass.  This is normal behavior which simply can not be eliminated.  For
those cases, we need to rely upon being able to re-enable interrupts and
allowing other operations to continue normally.  Simply put, in some
cases, nothing more can be done.

Thanks,
Robin
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