On 20 August 2012 21:42, Jens Axboe <axboe@xxxxxxxxx> wrote: > 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 > Jens kindly helped me a bit offline. My problem was due to the fact that I am booting off a FUSE virtual disk, and direct io won't work. I have now tested direct io using a natively formatted USB FLASH drive, and it's working fine. ;^) 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
