On 20 August 2012 20:57, Jens Axboe <axboe@xxxxxxxxx> wrote: > > On 08/20/2012 02:57 AM, Greg Sullivan wrote: > > I'm trying to do direct io (to avoid the file system cache) on Ubuntu > > i386. I've tried direct=1, and tried the io engines sync and libaio - > > it always seems to use the cache. > > > > Is there a way to bypass the file system cache on Ubuntu? I've got a > > vanilla install using the automated Ubuntu installer for Windows i386 > > 32-bit (dual boot). > > direct=1 will certainly bypass the cache on Linux, regardless of > version. What makes you suspect otherwise? > > -- > Jens Axboe Running a simple job that reads a 50MB file, the first time I run it, the aggregate throughput reported by fio is ~20MB/s For subsequent runs, the transfer rate is significantly higher - ~150MB/s. When I then clear the file system cache, and then run it again, the transfer rate drops back to 20MB/s. The INI: [read] bs=4k direct=1 sync=1 size=50M rw=read Just in case it's relevant, I'm running this on a very old laptop - a Compaq NW8000. (and 150MB/s is impossibly fast for it to be reading that from disk) Greg. -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
