On Tue, Jul 10, 2012 at 11:49:40AM +0200, Jan Kara wrote: > > =========================================================== > > Machine: arnold > > Result: http://www.csn.ul.ie/~mel/postings/mmtests-20120424/global-dhp__io-interactive-performance-ext3/arnold/comparison.html > > Arch: x86 > > CPUs: 1 socket, 2 threads > > Model: Pentium 4 > > Disk: Single Rotary Disk > > =========================================================== > > > > fsmark-single > > ------------- > > Completion times since 3.2 have been badly affected which coincides with > > the introduction of IO-less dirty page throttling. 3.3 was particularly > > bad. > > > > 2.6.32 was TERRIBLE in terms of read-latencies with the average latency > > and max latencies looking awful. The 90th percentile was close to 4 > > seconds and as a result the graphs are even more of a complete mess than > > they might have been otherwise. > > > > Otherwise it's worth looking closely at 3.0 and 3.2. In 3.0, 95% of the > > reads were below 206ms but in 3.2 this had grown to 273ms. The latency > > of the other 5% results increased from 481ms to 774ms. > > > > 3.4 is looking better at least. > > Yeah, 3.4 looks OK and I'd be interested in 3.5 results since I've merged > one more fix which should help the read latency. When 3.5 comes out, I'll be queue up the same tests. Ideally I would be running against each rc but the machines are used for other tests as well and these ones take too long for continual testing to be practical. > But all in all it's hard > to tackle the latency problems with ext3 - we have a journal which > synchronizes all the writes so we write to it with a high priority > (we use WRITE_SYNC when there's some contention on the journal). But that > naturally competes with reads and creates higher read latency. > Thanks for the good explanation. I'll just know to look out for this in interactivity-related or IO-latency bugs. > > <SNIP> > > ========================================================== > > Machine: hydra > > Result: http://www.csn.ul.ie/~mel/postings/mmtests-20120424/global-dhp__io-interactive-performance-ext3/hydra/comparison.html > > Arch: x86-64 > > CPUs: 1 socket, 4 threads > > Model: AMD Phenom II X4 940 > > Disk: Single Rotary Disk > > ========================================================== > > > > fsmark-single > > ------------- > > Completion times are all over the place with a big increase in 3.2 that > > improved a bit since but not as good as 3.1 kernels were. > > > > Unlike arnold, 2.6.32 is not a complete mess and makes a comparison more > > meaningful. Our maximum latencies have jumped around a lot with 3.2 > > being particularly bad and 3.4 not being much better. 3.1 and 3.3 were > > both good in terms of maximum latency. > > > > Average latency is shot to hell. In 2.6.32 it was 349ms and it's now 781ms. > > 3.2 was really bad but it's not like 3.0 or 3.1 were fantastic either. > > So I wonder what makes a difference between this machine and the previous > one. The results seem completely different. Is it the amount of memory? Is > it the difference in the disk? Or even the difference in the CPU? > Two big differences are 32-bit versus 64-bit and the 32-bit machine having 4G of RAM and the 64-bit machine having 8G. On the 32-bit machine, bounce buffering may have been an issue but as -S0 was specified (no sync) there would also be differences on when dirty page balancing took place. -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>