From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tony Battersby Subject: [PATCH] 3w-9xxx: fix abysmal write performance on some motherboards Date: Fri, 09 Nov 2007 13:04:35 -0500 Message-ID: <4734A133.8090207@cybernetics.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from host06.cybernetics.com ([206.246.200.22]:4330 "EHLO mail.cybernetics.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752174AbXKISEb (ORCPT ); Fri, 9 Nov 2007 13:04:31 -0500 Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: linuxraid@amcc.com, linux-scsi@vger.kernel.org The 3ware 9500S-8 SATA RAID controller exhibits terrible write performance when PCI memory-write-and-invalidate is disabled. This is easy to demonstrate by replacing pci_try_set_mwi() in the patch below with pci_clear_mwi(). My benchmarks show the following: MWI disabled: 15 MB/s write, 330 MB/s read MWI enabled: 240 MB/s write, 330 MB/s read Most motherboards will enable MWI without the driver having to set it explicitly, so most people probably wouldn't encounter this problem. For the few motherboards that don't enable it, this patch could give a 16x performance improvement for writing. This issue does not seem to affect the 9550SX controller, but the patch doesn't hurt it either. I haven't tested any of the other 3ware controllers. Signed-off-by: Tony Battersby --- --- linux-2.6.24-rc2/drivers/scsi/3w-9xxx.c.orig 2007-11-09 12:32:32.000000000 -0500 +++ linux-2.6.24-rc2/drivers/scsi/3w-9xxx.c 2007-11-09 12:33:20.000000000 -0500 @@ -2010,6 +2010,7 @@ static int __devinit twa_probe(struct pc } pci_set_master(pdev); + pci_try_set_mwi(pdev); if (pci_set_dma_mask(pdev, DMA_64BIT_MASK) || pci_set_consistent_dma_mask(pdev, DMA_64BIT_MASK))