We already tried running the SD interface at half speed to reduce power dissipation. It runs at full speed by default.
wad On Nov 17, 2009, at 12:49 PM, Peter Robinson wrote: > Hi Daniel, > >> Today I tried to figure out why running "sync" often takes 5-10 >> seconds >> or longer. This slows down suspend, where all data is synced to disk. >> In all cases that I looked at, the amount of data being synced was >> tiny. >> One example: in one run it had 160kB data to sync and it took 7.7 >> seconds. (blktrace is very handy for figuring this out) >> >> I traced this all the way to the SDHCI driver. These writes are >> typically small and scattered, and our hardware (or the card itself) >> takes a long time to process them. Many of the 1024 byte writes take >> 500-600ms. All other disk I/O is halted during these times. The >> delay is >> purely after submitting the SDHCI write command, and waiting for the >> completion interrupt to arrive. >> >> I then wrote a C application to reproduce the exact set of writes >> from a >> 20-second sync that I logged (using random data, but the same >> sectors, >> sizes and ordering) and reproduced the issue that way. >> >> I also moved the card over to my Dell laptop, ran the same program >> and >> saw the same (terrible) results. >> >> All info here: >> http://dev.laptop.org/ticket/9688 >> >> >> So, I have a feeling that at least with today's generation of miniSD >> cards we're going to be stuck with bad write performance, >> particularly >> for random-style access like this. >> >> One experiment that would be interesting to run would be to try >> this on >> one of the PhoenixBIOS boards, and then try it with the exact same SD >> card on a regular XO-1.5. Just in case... > > You might want to look at some of the SD/MMC frequency patches that he > applies to the kernel for the Nokia Internet tablet devices. I think > the default kernel defaults to a frequency half or even less than > half. The issue that might be encountered is that it doesn't always > work well on low quality SD cards but it would be at least worth > experimenting with it. > > His blog is here > http://intr.overt.org/blog/ > > The patches and a readme about them are here for the Nokia device (I > suspect they're just about the same everywhere). > http://intr.overt.org/5.2008.43-mmc-kernel/ > > Hope that can be of some help, or at least head you in the right > direction. > > Cheers, > Peter > _______________________________________________ > Devel mailing list > [email protected] > http://lists.laptop.org/listinfo/devel _______________________________________________ Devel mailing list [email protected] http://lists.laptop.org/listinfo/devel
