Chris, see bellow my answers --- On Mon, 1/4/10, Chris Worley <worleys@xxxxxxxxx> wrote: > From: Chris Worley <worleys@xxxxxxxxx> > Subject: Re: io scheduler merges control > To: "john smith" <whalajam@xxxxxxxxx> > Cc: fio@xxxxxxxxxxxxxxx > Date: Monday, January 4, 2010, 6:52 AM > 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. I'm doing 512B sequential reads. > Are you disabling the VM Cache w/ Direct I/O? Yes. > 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. I'm trying to compare two block drivers, when running "fio" I get from the first driver larger "iops" number but also larger "merges" number; the other driver has lower "iops" and no merges. Not sure why one driver has merges and the other doesn't but I'm trying to prevent merges (on both) in order to compare the drivers performance. John > 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 > -- 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
