On (17/01/08 13:50), Martin Knoblauch didst pronounce: > > <mail manglement snipped> > > The effect is defintely depending on the IO hardware. I performed the same tests > on a different box with an AACRAID controller and there things look different. I take it different also means it does not show this odd performance behaviour and is similar whether the patch is applied or not? > Basically > the "offending" commit helps seingle stream performance on that box, while dual/triple > stream are not affected. So I suspect that the CCISS is just not behaving well. > > And yes, the tests are usually done on a freshly booted box. Of course, I repeat them > a few times. On the CCISS box the numbers are very constant. On the AACRAID box > they vary quite a bit. > > I can certainly stress the box before doing the tests. Please define "many" for the kernel > compiles :-) > With 8GiB of RAM, try making 24 copies of the kernel and compiling them all simultaneously. Running that for for 20-30 minutes should be enough to randomise the freelists affecting what color of page is used for the dd test. > > > OK, the change happened between rc5 and rc6. Just following a > > > gut feeling, I reverted > > > > > > #commit 81eabcbe0b991ddef5216f30ae91c4b226d54b6d > > > #Author: Mel Gorman > > > #Date: Mon Dec 17 16:20:05 2007 -0800 > > > # > > > > > > > This has brought back the good results I observed and reported. > > > I do not know what to make out of this. At least on the systems > > > I care about (HP/DL380g4, dual CPUs, HT-enabled, 8 GB Memory, > > > SmartaArray6i controller with 4x72GB SCSI disks as RAID5 (battery > > > protected writeback cache enabled) and gigabit networking (tg3)) this > > > optimisation is a dissaster. > > > > > > > That patch was not an optimisation, it was a regression fix > > against 2.6.23 and I don't believe reverting it is an option. Other IO > > hardware benefits from having the allocator supply pages in PFN order. > > I think this late in the 2.6.24 game we just should leave things as they are. But > we should try to find a way to make CCISS faster, as it apparently can be faster. > > > Your controller would seem to suffer when presented with the same situation > > but I don't know why that is. I've added James to the cc in case he has seen this > > sort of situation before. > > > > > On the other hand, it is not a regression against 2.6.22/23. Those > > > > had bad IO scaling to. It would just be a shame to loose an apparently > > > > great performance win. > > > > Could you try running your tests again when the system has been > > stressed with some other workload first? > > > > Will do. > Thanks -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab - 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
