linux-kernel - Re: Overview of concurrency managed workqueue

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Message-Id: <20100618003127.10d9e6c8.akpm@linux-foundation.org>
Date:	Fri, 18 Jun 2010 00:31:27 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Andy Walls <awalls@...metrocast.net>,
	Daniel Walker <dwalker@...eaurora.org>, mingo@...e.hu,
	linux-kernel@...r.kernel.org, jeff@...zik.org,
	rusty@...tcorp.com.au, cl@...ux-foundation.org,
	dhowells@...hat.com, arjan@...ux.intel.com,
	johannes@...solutions.net, oleg@...hat.com, axboe@...nel.dk
Subject: Re: Overview of concurrency managed workqueue

On Fri, 18 Jun 2010 09:16:15 +0200 Tejun Heo <tj@...nel.org> wrote:

> On 06/18/2010 01:16 AM, Andrew Morton wrote:
> > On Thu, 17 Jun 2010 08:01:06 -0400
> > Andy Walls <awalls@...metrocast.net> wrote:
> > 
> >> I'm going to agree with Tejun, that tweaking worker thread priorities
> >> seems like an odd thing, since they are meant to handle deferable
> >> actions - things that can be put off until later.
> > 
> > Disagree.  If you're in an interrupt handler and have some work which
> > you want done in process context and you want it done RIGHT NOW then
> > handing that work off to a realtime-policy worker thread is a fine way of
> > doing that.
> 
> In that case, the right thing to do would be using threaded interrupt
> handler.  It's not only easier but also provide enough context such
> that RT kernel can do the right thing.

Nope.  Consider a simple byte-at-a-time rx handler.  The ISR grabs the
byte, stashes it away, bangs on the hardware a bit then signals
userspace to promptly start processing that byte.  Very simple,
legitimate and a valid thing to do.

Also the "interrupt" code might be running from a timer handler.  Or it
might just be in process context, buried in a forest of locks and wants
to punt further processing into a separate process.

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