Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755261AbYJNXSy (ORCPT ); Tue, 14 Oct 2008 19:18:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752780AbYJNXSP (ORCPT ); Tue, 14 Oct 2008 19:18:15 -0400 Received: from aeryn.fluff.org.uk ([87.194.8.8]:43032 "EHLO kira.home.fluff.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752584AbYJNXSM (ORCPT ); Tue, 14 Oct 2008 19:18:12 -0400 Message-Id: <20081014231810.755306687@fluff.org.uk> References: <20081014231714.739345038@fluff.org.uk> User-Agent: quilt/0.46-1 Date: Wed, 15 Oct 2008 00:17:18 +0100 From: ben@fluff.org.uk To: linux-kernel@vger.kernel.org Cc: drzeus-mmc@drzeus.cx, Ben Dooks Subject: [patch 4/5] s3cmci: fix continual accesses to host->pio_ptr Content-Disposition: inline; filename=simtec/s3c24xx-mmc-faster-transfer-core.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2391 Lines: 82 The s3cmci driver uses the host->pio_ptr field to point to the current position into the buffer for data transfer. During the transfers it does the following: while (fifo_words--) *(host->pio_ptr++) = readl(from_ptr); This is inefficent, as host->pio_ptr is not used in any other part of the transfer but the compiler emits code which does the following: while (fifo_words--) { u32 *ptr = host->pio_ptr; *ptr = readl(from_ptr); ptr++; host->pio_ptr = ptr; } This is obviously a waste of a load and store each time around the loop, which could be up to 16 times depending on how much needs to be transfered. Move the ptr accesses to outside the while loop so that we do not end up reloading/re-writing the pointer. Note, this seems to make the code 16 bytes larger. Signed-off-by: Ben Dooks Index: linux-2.6.27-rc5-quilt1/drivers/mmc/host/s3cmci.c =================================================================== --- linux-2.6.27-rc5-quilt1.orig/drivers/mmc/host/s3cmci.c 2008-09-08 16:50:27.000000000 +0100 +++ linux-2.6.27-rc5-quilt1/drivers/mmc/host/s3cmci.c 2008-09-08 16:52:21.000000000 +0100 @@ -238,6 +238,7 @@ static void do_pio_read(struct s3cmci_ho { int res; u32 fifo; + u32 *ptr; u32 fifo_words; void __iomem *from_ptr; @@ -283,8 +284,10 @@ static void do_pio_read(struct s3cmci_ho host->pio_count += fifo; fifo_words = fifo >> 2; + ptr = host->pio_ptr; while (fifo_words--) - *(host->pio_ptr++) = readl(from_ptr); + *ptr++ = readl(from_ptr); + host->pio_ptr = ptr; if (fifo & 3) { u32 n = fifo & 3; @@ -319,6 +322,7 @@ static void do_pio_write(struct s3cmci_h void __iomem *to_ptr; int res; u32 fifo; + u32 *ptr; to_ptr = host->base + host->sdidata; @@ -353,8 +357,10 @@ static void do_pio_write(struct s3cmci_h host->pio_count += fifo; fifo = (fifo + 3) >> 2; + ptr = host->pio_ptr; while (fifo--) - writel(*(host->pio_ptr++), to_ptr); + writel(*ptr++, to_ptr); + host->pio_ptr = ptr; } enable_imask(host, S3C2410_SDIIMSK_TXFIFOHALF); -- Ben (ben@fluff.org, http://www.fluff.org/) 'a smiley only costs 4 bytes' -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/