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    SubjectRE: [PATCH] fsldma: fix performance degradation by optimizing spinlock use.
    Date
    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@freescale.com>

    - Leo

    > -----Original Message-----
    > From: Shi Xuelin-B29237
    > Sent: Thursday, April 26, 2012 10:04 AM
    > To: dan.j.williams@intel.com
    > Cc: vinod.koul@intel.com; linuxppc-dev@lists.ozlabs.org; linux-
    > kernel@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@ovro.caltech.edu]
    > Sent: 2012年1月12日 0:14
    > 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.
    >
    > 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 <b29237@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@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
    > >
    > >

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