From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: bnx2 fails to compile on parisc because of missing get_dma_ops() Date: Thu, 17 Jun 2010 08:12:16 -0500 Message-ID: <1276780336.2789.6.camel@mulgrave.site> References: Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: 'FUJITA Tomonori' , "vapier@gentoo.org" , "netdev@vger.kernel.org" , "linux-parisc@vger.kernel.org" , "linux-kernel@vger.kernel.org" To: Michael Chan Return-path: In-Reply-To: Sender: linux-parisc-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Thu, 2010-06-17 at 05:54 -0700, Michael Chan wrote: > FUJITA Tomonori wrote: > > > From: FUJITA Tomonori > > Date: Thu, 17 Jun 2010 13:06:15 +0900 > > Subject: [PATCH] bnx2: fix dma_get_ops compilation breakage > > > > This removes dma_get_ops() prefetch optimization in bnx2. > > > > bnx2 uses dma_get_ops() to see if dma_sync_single_for_cpu() is > > noop. bnx2 does prefetch if it's noop. > > > > But dma_get_ops() isn't available on all the architectures (only the > > architectures that uses dma_map_ops struct have it). Using > > dma_get_ops() in drivers leads to compilation breakage on many > > archtectures. > > > > Currently, we don't have a way to see if dma_sync_single_for_cpu() is > > noop. If it can improve the performance notably, we can add the new > > DMA API for it. > > This prefetch improves performance noticeably when the driver is > handling incoming 64-byte packets at a sustained rate. So why not do it unconditionally? The worst that can happen is that you pull in a stale cache line which will get cleaned in the dma_sync, thus slightly degrading performance on incoherent architectures. Alternatively, come up with a dma prefetch infrastructure ... all you're really doing is hinting to the architecture that you'll sync this region next. James