From mboxrd@z Thu Jan 1 00:00:00 1970 From: benh@kernel.crashing.org (Benjamin Herrenschmidt) Date: Sat, 30 Apr 2011 08:55:06 +1000 Subject: [Linaro-mm-sig] [RFC] ARM DMA mapping TODO, v1 In-Reply-To: References: <201104212129.17013.arnd@arndb.de> <20110428093039.GU17290@n2100.arm.linux.org.uk> <1304024836.2513.198.camel@pasglop> <201104291326.25634.arnd@arndb.de> <4DBAA9B4.3070306@vmware.com> Message-ID: <1304117706.2513.269.camel@pasglop> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Fri, 2011-04-29 at 09:34 -0400, Jerome Glisse wrote: > > Radeon memory controller can do non snooped pci transaction, as far as > i have tested most of the x86 pci bridge don't try to be coherent then > ie they don't analyze pci dma and ask for cpu flush they just perform > the request (and i guess it's what all bridge will do), so it endup > being noncoherent. I haven't done any benchmark of how faster it's for > the GPU when it's not snooping but i guess it can give 50% boost as it > likely drastictly reduce pci transaction overhead. > > I am talking here about device that you plug into any pci or pcie > slot, so it's not igp integrated into northbridge or into the cpu. Right, the card has nothing to do with the snooping process, it's purely a feature of the bridge, based on a flag optionally set by the card. As I said earlier, bridges have the freedom to ignore it, which we do on ppc, so that's a non issue. Cheers, Ben.