From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from DB3EHSOBE005.bigfish.com (db3ehsobe005.messaging.microsoft.com [213.199.154.143]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (Client CN "mail.global.frontbridge.com", Issuer "Microsoft Secure Server Authority" (verified OK)) by ozlabs.org (Postfix) with ESMTPS id 6F6B51007D2 for ; Tue, 22 Nov 2011 17:11:02 +1100 (EST) From: To: , , , Subject: [PATCH][RFC] fsldma: fix performance degradation by optimizing spinlock use. Date: Tue, 22 Nov 2011 12:55:05 +0800 Message-ID: <1321937705-19587-1-git-send-email-b29237@freescale.com> MIME-Version: 1.0 Content-Type: text/plain Cc: Forrest Shi , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Forrest Shi 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. I believe it has no neglect impact on the following call of dma_async_is_complete(...). we can see below three conditions will be identified as success a) x < complete < use b) x < complete+N < use+N c) x < complete < use+N here complete is the completed_cookie, use is the last_used cookie, x is the querying cookie, N is MAX cookie when chan->completed_cookie is being read, the last_used may be incresed. Anyway it has no neglect impact on the dma status decision. Signed-off-by: Forrest Shi --- drivers/dma/fsldma.c | 5 ----- 1 files changed, 0 insertions(+), 5 deletions(-) diff --git a/drivers/dma/fsldma.c b/drivers/dma/fsldma.c index 8a78154..1dca56f 100644 --- a/drivers/dma/fsldma.c +++ b/drivers/dma/fsldma.c @@ -986,15 +986,10 @@ 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; 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