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 degr=
adation.
Anyway it is acceptable for me. Do you have any other comments?

Thanks,
Forrest

-----Original Message-----
From: Shi Xuelin-B29237=20
Sent: 2011=1B$BG/=1B(B12=1B$B7n=1B(B26=1B$BF|=1B(B 14:01
To: iws@ovro.caltech.edu; vinod.koul@intel.com; dan.j.williams@intel.com; l=
inuxppc-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 <redacted>

    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 [off-list ref]
---
 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..008=

fb5e 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 =3D to_fsl_chan(dchan);
 	dma_cookie_t last_complete;
 	dma_cookie_t last_used;
-	unsigned long flags;
-
-	spin_lock_irqsave(&chan->desc_lock, flags);
=20
	last_complete =3D chan->completed_cookie;
+	smp_mb();
	last_used =3D dchan->cookie;
=20
-	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