linux-kernel - Re: workqueue thing

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Date:	Wed, 23 Dec 2009 05:25:44 -0500
From:	Jeff Garzik <jeff@...zik.org>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, awalls@...ix.net,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	jens.axboe@...cle.com, rusty@...tcorp.com.au,
	cl@...ux-foundation.org, dhowells@...hat.com,
	arjan@...ux.intel.com, avi@...hat.com, johannes@...solutions.net,
	andi@...stfloor.org
Subject: Re: workqueue thing

On 12/23/2009 03:41 AM, Peter Zijlstra wrote:
> On Wed, 2009-12-23 at 01:13 -0500, Jeff Garzik wrote:
>> On 12/23/2009 01:02 AM, Ingo Molnar wrote:
>>> One key thing i havent seen in this discussion are actual measurements. I
>>> think a lot could be decided by simply testing this patch-set, by looking at
>>> the hard numbers: how much faster (or slower) did a particular key workload
>>> get before/after these patches.
>>
>> We are dealing with situations where drivers are using workqueues to
>> provide a sleep-able context, and trying to solve problems related to that.
>
> So why are threaded interrupts not considered? Isn't the typical atomic
> context of drivers the IRQ handler?


I don't see a whole lot of driver authors rushing to support threaded 
interrupts.  It is questionable whether the myriad crazy IDE interrupt 
routing schemes are even compatible.  Thomas's Mar 23 2009 email says 
"the primary handler must disable the interrupt at the device level" 
That is not an easy request for all the hardware libata must support.

But the most obvious reason is also the most compelling:  Tejun's work 
maps precisely to libata's needs.  And his work would seem to mesh well 
with other drivers in similar situations.

	Jeff


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