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). Arnd -- 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
