On 2010-12-23 14:51, Russell King - ARM Linux wrote: > On Thu, Dec 23, 2010 at 02:41:26PM +0100, Michal Nazarewicz wrote: >> Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> writes: >>> Has anyone addressed my issue with it that this is wide-open for >>> abuse by allocating large chunks of memory, and then remapping >>> them in some way with different attributes, thereby violating the >>> ARM architecture specification? >>> >>> In other words, do we _actually_ have a use for this which doesn't >>> involve doing something like allocating 32MB of memory from it, >>> remapping it so that it's DMA coherent, and then performing DMA >>> on the resulting buffer? >> Huge pages. >> >> Also, don't treat it as coherent memory and just flush/clear/invalidate >> cache before and after each DMA transaction. I never understood what's >> wrong with that approach. > If you've ever used an ARM system with a VIVT cache, you'll know what's > wrong with this approach. > > ARM systems with VIVT caches have extremely poor task switching > performance because they flush the entire data cache at every task switch > - to the extent that it makes system performance drop dramatically when > they become loaded. > > Doing that for every DMA operation will kill the advantage we've gained > from having VIPT caches and ASIDs stone dead. This statement effectively means: don't map dma-able memory to the CPU unless it's uncached. Have I missed anything? > -- > To unsubscribe from this list: send the line "unsubscribe linux-media" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>