linux-kernel - Re: RFC: Allow block drivers to poll for I/O instead of sleeping

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Message-ID: <20130625001102.GA6623@home.goodmis.org>
Date:	Mon, 24 Jun 2013 20:11:02 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Ingo Molnar <mingo@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-nvme@...ts.infradead.org,
	Linux SCSI List <linux-scsi@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: RFC: Allow block drivers to poll for I/O instead of sleeping

On Mon, Jun 24, 2013 at 09:17:18AM +0200, Jens Axboe wrote:
> On Sun, Jun 23 2013, Linus Torvalds wrote:
> > 
> > You could try to do that either *in* the idle thread (which would take
> > the context switch overhead - maybe negating some of the advantages),
> > or alternatively hook into the scheduler idle logic before actually
> > doing the switch.
> 
> It can't happen in the idle thread. If you need to take the context
> switch, then you've negated pretty much all of the gain of the polled
> approach.

What about hooking into the idle_balance code? That happens if we are
about to go to idle but before the full schedule switch to the idle
task.


In __schedule(void):

	if (unlikely(!rq->nr_running))
		idle_balance(cpu, rq);

-- Steve

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