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From: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
To: Nick Piggin <npiggin@suse.de>
Cc: "Siddha, Suresh B" <suresh.b.siddha@intel.com>,
	Christoph Lameter <clameter@sgi.com>,
	linux-kernel@vger.kernel.org, arjan@linux.intel.com,
	mingo@elte.hu, ak@suse.de, jens.axboe@oracle.com,
	James.Bottomley@SteelEye.com, andrea@suse.de,
	akpm@linux-foundation.org, andrew.vasquez@qlogic.com
Subject: Re: [rfc] direct IO submission and completion scalability issues
Date: Tue, 31 Jul 2007 17:55:13 -0700	[thread overview]
Message-ID: <20070801005513.GE10033@linux-os.sc.intel.com> (raw)
In-Reply-To: <20070801004117.GE31006@wotan.suse.de>

On Wed, Aug 01, 2007 at 02:41:18AM +0200, Nick Piggin wrote:
> On Tue, Jul 31, 2007 at 10:14:03AM -0700, Suresh B wrote:
> > Yes, softirq context is one way. But just didn't want to penalize the running
> > task by taking away some of its cpu time. With CFS micro accounting, perhaps
> > we can track irq, softirq time and avoid penalizing the running task's cpu
> > time.
> 
> But you "penalize" the running task in the completion handler as well
> anyway.

Yes.

Ingo, in general with CFS micro accounting, we should be able to avoid
penalizing the running task by tracking irq/softirq time. Isn't it?

> Doing this with a SCHED_FIFO task is sort of like doing interrupt
> threading which AFAIK has not been accepted (yet).

I am not recommending SCHED_FIFO. I will take a look at softirq
infrastructure for this.

> > This workload is using direct IO and there is no batching at the block layer
> > for direct IO. IO is submitted to the HW as it arrives.
> 
> So you aren't putting concurrent requests into the queue? Sounds like
> userspace should be improved.

Nick remember that there are hundreds of disks in this setup and at
an instance, there will be max 1 or 2 requests per disk.

> > It is applicable for both direct IO and buffered IO. But the implementations
> > will differ. For example in buffered IO, we can setup in such a way that the
> > block plug timeout function runs on the IO completion cpu.
> 
> It would be nice to be doing that anyway. But unplug via request submission
> rather than timeout is fairly common in buffered loads too.

Ok. Currently the patch handles both direct and buffered IO. While making
improvements to this patch I will make sure that both the paths take
advantage of this.

thanks,
suresh

  reply	other threads:[~2007-08-01  1:01 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-07-28  1:21 Siddha, Suresh B
2007-07-30 18:20 ` Christoph Lameter
2007-07-30 20:35   ` Siddha, Suresh B
2007-07-31  4:19     ` Nick Piggin
2007-07-31 17:14       ` Siddha, Suresh B
2007-08-01  0:41         ` Nick Piggin
2007-08-01  0:55           ` Siddha, Suresh B [this message]
2007-08-01  1:24             ` Nick Piggin
2008-02-03  9:52 ` Nick Piggin
2008-02-03 10:53   ` Pekka Enberg
2008-02-03 11:58     ` Nick Piggin
2008-02-04  2:10   ` David Chinner
2008-02-04  4:14     ` Arjan van de Ven
2008-02-04  4:40       ` David Chinner
2008-02-04 10:09         ` Nick Piggin
2008-02-05  0:14           ` David Chinner
2008-02-08  7:50             ` Nick Piggin
2008-02-04 18:21     ` Zach Brown
2008-02-04 20:10       ` Jens Axboe
2008-02-04 21:45         ` Arjan van de Ven
2008-02-05  8:24           ` Jens Axboe
2008-02-04 10:12   ` Jens Axboe
2008-02-04 10:31     ` Nick Piggin
2008-02-04 10:33       ` Jens Axboe
2008-02-04 22:28         ` James Bottomley
2008-02-04 10:30   ` Andi Kleen
2008-02-04 21:47   ` Siddha, Suresh B

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