On Tue, May 11, 2010 at 07:30:15PM -0400, John Watlington wrote: > On May 11, 2010, at 7:24 PM, James Cameron wrote: > > On Tue, May 11, 2010 at 07:14:53PM -0400, John Watlington wrote: > >> Writes in UNIX are typically asynchronous --- get the data into a memory > >> buffer and the program can continue along its merry way. > >> I strongly suspect that writes through the SD system are forced to wait > >> for the media to complete the write. > > > > My tests show that our kernel is doing this for USB and SD, on ext2, > > ext3, ext4, vfat, and raw access to the block device (open ... write ... > > write ... close). It isn't doing it for writes to tmpfs or null. > > Are sync writes forced on removable media ?
No. Most writes pass in a time consistent with caching, and the latency is so small that I'm certain they aren't reaching the media (60us). It's only some writes that are delayed by 600ms to 3000ms. -- James Cameron http://quozl.linux.org.au/ _______________________________________________ Devel mailing list [email protected] http://lists.laptop.org/listinfo/devel
