[PATCH] fsldma: fix performance degradation by optimizing spinlock use.

[Li Yang-R58472]

Hi Dan and Vinod,

Please help to pick this patch up.  It addresses a great performance regression for RAID offloading.

Acked-by: Li Yang <leoli at freescale.com>

- Leo

> -----Original Message-----
> From: Shi Xuelin-B29237
> Sent: Thursday, April 26, 2012 10:04 AM
> To: dan.j.williams at intel.com
> Cc: vinod.koul at intel.com; linuxppc-dev at lists.ozlabs.org; linux-
> kernel at vger.kernel.org; Ira W. Snyder; Li Yang-R58472
> Subject: RE: [PATCH] fsldma: fix performance degradation by optimizing
> spinlock use.
> 
> Hi Dan Williams,
> 
> Do you have any comment about this patch?
> 
> Thanks,
> Forrest
> 
> -----Original Message-----
> From: Ira W. Snyder [mailto:iws at ovro.caltech.edu]
> Sent: 2012年1月12日 0:14
> To: Shi Xuelin-B29237
> Cc: vinod.koul at intel.com; dan.j.williams at intel.com; linuxppc-
> dev at lists.ozlabs.org; linux-kernel at vger.kernel.org
> Subject: Re: [PATCH] fsldma: fix performance degradation by optimizing
> spinlock use.
> 
> 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 at ovro.caltech.edu; vinod.koul at intel.com;
> dan.j.williams at intel.com; linuxppc-dev at lists.ozlabs.org; linux-
> kernel at vger.kernel.org
> > Cc: Shi Xuelin-B29237
> > Subject: [PATCH] fsldma: fix performance degradation by optimizing
> spinlock use.
> >
> > From: Forrest shi <b29237 at freescale.com>
> >
> >     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 <xuelin.shi at freescale.com>
> > ---
> >  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
> >
> >