On Thu, Dec 24, 2009 at 12:12 PM, john smith <whalajam@xxxxxxxxx> wrote: > IOPS-reported numbers for a test vary (more than 30% in my case) from one run to another depending on kernel io scheduler merges (reported in "Disk stats/merges=reads/writes") making it hard to measure/compare performance of block drivers, for instance. Are you trying to measure sequential I/O? Most application traces I've seen show that despite the sequential/random mix reported, the vast majority of "sequential" accesses are two blocks. Of course this isn't true for applications that only do logging and a few others... but, it means that for most applications, there really isn't any sequential access to worry about. Are you disabling the VM Cache w/ Direct I/O? Maybe tell us more about what you're trying to test. It may be more a matter of control and preconditioning than a fio issue. Chris > > I don't see any way to turn off kernel io scheduler merges (cfq or others) > and I'd ask if you would consider adding support for it, disabling the merges per individual device, using sys-fs maybe? > > If you do, adding an option to fio for controlling the merges would be useful too, > > thanks, > John > > > > > -- > 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 > -- 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
