On Wed, Mar 31, 2010 at 6:02 PM, Keith Mannthey <kmannth@xxxxxxxxxx> wrote: > On Tue, 2010-03-30 at 23:06 -0500, Eric Sandeen wrote: >> Keith Mannthey wrote: >> > On Mon, 2010-03-29 at 11:10 -0400, Greg Freemyer wrote: >> >> On Mon, Mar 29, 2010 at 2:25 AM, Keith Mannthey <kmannth@xxxxxxxxxx> wrote: >> >>> >> >>> After 2.6.30 I am seeing large performance regressions on a raid setup. >> >>> I am working to publish a larger amount of data but I wanted to get some >> >>> quick data out about what I am seeing. >> >>> >> >> Is mdraid involved? >> >> >> >> They added barrier support for some configs after 2.6.30 I believe. >> >> It can cause a drastic perf change, but it increases reliability and >> >> is "correct". >> > >> > lvm and device mapper are is involved. The git bisect just took me to: >> > >> > 374bf7e7f6cc38b0483351a2029a97910eadde1b is first bad commit >> > commit 374bf7e7f6cc38b0483351a2029a97910eadde1b >> > Author: Mikulas Patocka <mpatocka@xxxxxxxxxx> >> > Date: Mon Jun 22 10:12:22 2009 +0100 >> > >> > dm: stripe support flush >> > >> > Flush support for the stripe target. >> > >> > This sets ti->num_flush_requests to the number of stripes and >> > remaps individual flush requests to the appropriate stripe devices. >> > >> > Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> >> > Signed-off-by: Alasdair G Kergon <agk@xxxxxxxxxx> >> > >> > :040000 040000 542f4b9b442d1371c6534f333b7e00714ef98609 d490479b660139fc1b6b0ecd17bb58c9e00e597e M drivers >> > >> > >> > This may be correct behavior but the performance penalty in this test >> > case is pretty high. >> > >> > I am going to move back to current kernels and starting looking into >> > ext4/dm flushing. >> >> It would probably be interesting to do a mount -o nobarrier to see if >> that makes the regression go away. > > -o nobarrier takes the regression away with 2.6.34-rc3: > > Default mount: ~27500 > > -o nobarrier: ~12500 > > Barriers on this setup cost ALOT during writes. > > Interestingly as well the "mailserver" workload regression is also > removed by mounting with "-o nobarrier". > > I am going to see what impact is seen on a single disk setup. > > Thanks, > Keith Mannthey > LTC FS-Dev I'm curious if your using an internal or external journal? I'd guess the cost of barriers is much greater with an internal journal, but I don't recall seeing any benchmarks one way or the other. Greg -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
