On 08/20/2012 01:37 PM, Greg Sullivan wrote: > 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) Please run fio with strace -o somefile -f fio <ini.file> and bzip2+send the 'somefile' file. -- Jens Axboe -- 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
