On Wed, Sep 28, 2011 at 10:34 PM, Praveen G K <praveen.gk@xxxxxxxxx> wrote: > The problem is I am seeing write > speeds of about 5MBps on a Sandisk eMMC product and I can clearly see > the time lost when measured between sending a command and receiving a > data irq. I am not sure what kind of an issue this is. 5MBps feels > really slow but can the internal housekeeping of the card take so much > time? It can indeed take as much time as it wants as long as it meets the specifications, what does your datasheet say? If you connect a signal analyzer to your MMC bus you *will* know for sure whether this is actually caused by the card, of if there is some kernel irq/workqueue latency involved. If the card is the issue, what you can do to improve performance is to look for other eMMC vendors... ;-) > I mean, for the usual transfers it takes about 3ms to transfer > 64kB of data, but for the 63rd and 64th transfers, it takes 250 ms. > The thing is this is not on a file system. I am measuring the speed > using basic "dd" command to write directly to the block device. Have you tried to make a deeper analysis of the card characteristics using Arnd Bergmanns "flashbench" tool? http://git.linaro.org/gitweb?p=people/arnd/flashbench.git;a=summary There you will see for sure if there are some problematic read boundaries on this specific card. Yours, Linus Walleij -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
