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?
Thanks,
Forrest
-----Original Message-----
From: Shi Xuelin-B29237
Sent: 2011年12月26日 14:01
To: i...@ovro.caltech.edu; vinod.k...@intel.com; dan.j.willi...@intel.com;
linuxppc-dev@lists.ozlabs.org; linux-ker...@vger.kernel.org
Cc: Shi Xuelin-B29237
Subject: [PATCH] fsldma: fix performance degradation by optimizing spinlock use.
From: Forrest shi <b29...@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....@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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