Re: [PATCH] fsldma: fix performance degradation by optimizing spinlock use.
From: Ira W. Snyder <hidden>
Date: 2012-01-11 16:45:05
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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
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-----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 <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..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