On Mon, Mar 21, 2011 at 11:55:36PM +0100, Arnd Bergmann wrote: > On Monday 21 March 2011 23:38:56 Simon Horman wrote: > > Write Speed > > # dd if=/dev/zero of=/dev/mmcblk0 bs=512 count=100000 > > SD1.1: 2.5 MB/s <-- Faster than expected > > SD2.0: 3.0 MB/s <-- Faster than expected > > SDHC Class 2: 2.3 MB/s <-- Faster than expected > > SDHC Class 10: 4.0 MB/s <-- Slower than expected > > SanDisk SDHC Class 10: 4.3 MB/s <-- Slower than expected > > MMC4.0: 2.3 MB/s <-- Clocked down to 12Mhz due to > > driver limitations > > Please see https://lwn.net/Articles/428584/ and https://wiki.linaro.org/WorkingGroups/KernelConsolidation/Projects/FlashCardSurvey > for possible explanations why your speed is not what you think > it should be. > > I have written a tool that will give you more conclusive > data: git clone git://git.linaro.org/people/arnd/flashbench.git > > Please Cc flashbench-results@xxxxxxxxxxxxxxxx when you have > measurements from that. You will first need to find out > the erase block size of each card (typically 4 MB), and then > pass that to the --open-au --erasesize=${SIZE} --open-au-nr=${NR} > benchmark to get useful results. > > The write speed for writing full erase blocks (allocation units) > is normally the best that a card can provide, and you will see > how it gets worse with smaller block sizes. Try different > values for ${NR} to find out what the maximum is that the card > can sustain at full performance, most cards get really slow as > soon as it runs out of segments (not the case with your > benchmarking, since you write from start to end). Thanks Arnd, I'll report back once I have some numbers. -- 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
