On Tue, Jul 1, 2008 at 8:55 PM, Gadiyar, Anand <gadiyar@xxxxxx> wrote: > <snip> > >> Actually, I don't have any detail information about the IP from mentor of Blackfin. >> I just found the instruction from the Blackfin manual. We need to clear DMA IRQ flag >> manually on Blackfin, although it is not true on Davinci. >> >> > >> >> > > But when I tried to write large file to the U-DISK >> >> > > (such as 10Mbyte or 100Mbyte), speed is very slow and mush >> >> > > slower than PIO mode, IMO. >> > >> > I've certainly seen that "little" problem. I couldn't tell >> > if the root cause was from Mentor's DMA support or from the >> > kind of USB-antagonistic DMA engine on DaVinci, but when the >> > DMA logic has to generate an IRQ for each packet (to get sane >> > semantics), it's hopeless getting good throughput unless it's >> > dirt cheap to set up and complete DMA transfers. (It isn't.) >> > >> > As has been seen elsewhere: when the cost of DMA integration >> > exceeds the cost to stuff the FIFO by hand, DMA is not a win. >> > That's an issue with the drivers/dma framework sometimes too, >> > though in that case the issue is purely software. >> > >> >> I did lots of test to compare the DMA and PIO such as a) dd large file >> to a USB flash disk, b) use bonnie++ to do performance test. >> The result is that no throughput improvement on DMA and CPU >> consumption is the same as PIO. >> >> We hope to see the CPU usage of DMA mode is less than PIO mode, but >> didn't got the expectation. > > Approximately how much is the performance you see with PIO mode (given that you also see the same with DMA mode)? > I recorded the bonnie++ result in our tracker: https://blackfin.uclinux.org/gf/project/uclinux-dist/tracker/?action=TrackerItemEdit&tracker_item_id=3786 > Any chance you have dynamic tick suppression enabled (CONFIG_NO_HZ)? > If so, could you try with nohz=off in your bootargs? > Is this helpful? I am afraid that dynamic tick is not fully supported on Blackfin. But I will try it. Thanks -Bryan -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
