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