From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757761Ab2AKQpF (ORCPT ); Wed, 11 Jan 2012 11:45:05 -0500 Received: from ovro.ovro.caltech.edu ([192.100.16.2]:34637 "EHLO ovro.ovro.caltech.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757627Ab2AKQpD (ORCPT ); Wed, 11 Jan 2012 11:45:03 -0500 X-Greylist: delayed 1874 seconds by postgrey-1.27 at vger.kernel.org; Wed, 11 Jan 2012 11:45:03 EST Date: Wed, 11 Jan 2012 08:13:47 -0800 From: "Ira W. Snyder" To: Shi Xuelin-B29237 Cc: "vinod.koul@intel.com" , "dan.j.williams@intel.com" , "linuxppc-dev@lists.ozlabs.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] fsldma: fix performance degradation by optimizing spinlock use. Message-ID: <20120111161347.GA1430@ovro.caltech.edu> References: <1324879263-11845-1-git-send-email-b29237@freescale.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.6 (ovro.ovro.caltech.edu); Wed, 11 Jan 2012 08:13:49 -0800 (PST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 11, 2012 at 07:54:55AM +0000, Shi Xuelin-B29237 wrote: > Hello Iris, > > As we discussed in the previous patch, I add one smp_mb() in fsl_tx_status. > In my testing with iozone, this smp_mb() could cause 1%~2% performance degradation. > Anyway it is acceptable for me. Do you have any other comments? > This patch looks fine to me. Ira > -----Original Message----- > From: Shi Xuelin-B29237 > Sent: 2011年12月26日 14:01 > To: iws@ovro.caltech.edu; vinod.koul@intel.com; dan.j.williams@intel.com; linuxppc-dev@lists.ozlabs.org; linux-kernel@vger.kernel.org > Cc: Shi Xuelin-B29237 > Subject: [PATCH] fsldma: fix performance degradation by optimizing spinlock use. > > From: Forrest shi > > dma status check function fsl_tx_status is heavily called in > a tight loop and the desc lock in fsl_tx_status contended by > the dma status update function. this caused the dma performance > degrades much. > > this patch releases the lock in the fsl_tx_status function, and > introduce the smp_mb() to avoid possible memory inconsistency. > > Signed-off-by: Forrest Shi > --- > drivers/dma/fsldma.c | 6 +----- > 1 files changed, 1 insertions(+), 5 deletions(-) > > diff --git a/drivers/dma/fsldma.c b/drivers/dma/fsldma.c index 8a78154..008fb5e 100644 > --- a/drivers/dma/fsldma.c > +++ b/drivers/dma/fsldma.c > @@ -986,15 +986,11 @@ static enum dma_status fsl_tx_status(struct dma_chan *dchan, > struct fsldma_chan *chan = to_fsl_chan(dchan); > dma_cookie_t last_complete; > dma_cookie_t last_used; > - unsigned long flags; > - > - spin_lock_irqsave(&chan->desc_lock, flags); > > last_complete = chan->completed_cookie; > + smp_mb(); > last_used = dchan->cookie; > > - spin_unlock_irqrestore(&chan->desc_lock, flags); > - > dma_set_tx_state(txstate, last_complete, last_used, 0); > return dma_async_is_complete(cookie, last_complete, last_used); } > -- > 1.7.0.4 > >