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

From: b29237
Date: Mon Dec 26 2011 - 01:49:40 EST

From: Forrest shi <b29237@xxxxxxxxxxxxx>

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@xxxxxxxxxxxxx>
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);

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