Messages in this thread | | | Subject | Re: [performance bug] kernel building regression on 64 LCPUs machine | From | "Alex,Shi" <> | Date | Mon, 14 Feb 2011 10:25:18 +0800 |
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On Sun, 2011-02-13 at 02:25 +0800, Corrado Zoccolo wrote: > On Sat, Feb 12, 2011 at 10:21 AM, Alex,Shi <alex.shi@intel.com> wrote: > > On Wed, 2011-01-26 at 16:15 +0800, Li, Shaohua wrote: > >> On Thu, Jan 20, 2011 at 11:16:56PM +0800, Vivek Goyal wrote: > >> > On Wed, Jan 19, 2011 at 10:03:26AM +0800, Shaohua Li wrote: > >> > > add Jan and Theodore to the loop. > >> > > > >> > > On Wed, 2011-01-19 at 09:55 +0800, Shi, Alex wrote: > >> > > > Shaohua and I tested kernel building performance on latest kernel. and > >> > > > found it is drop about 15% on our 64 LCPUs NHM-EX machine on ext4 file > >> > > > system. We find this performance dropping is due to commit > >> > > > 749ef9f8423054e326f. If we revert this patch or just change the > >> > > > WRITE_SYNC back to WRITE in jbd2/commit.c file. the performance can be > >> > > > recovered. > >> > > > > >> > > > iostat report show with the commit, read request merge number increased > >> > > > and write request merge dropped. The total request size increased and > >> > > > queue length dropped. So we tested another patch: only change WRITE_SYNC > >> > > > to WRITE_SYNC_PLUG in jbd2/commit.c, but nothing effected. > >> > > since WRITE_SYNC_PLUG doesn't work, this isn't a simple no-write-merge issue. > >> > > > >> > > >> > Yep, it does sound like reduce write merging. But moving journal commits > >> > back to WRITE, then fsync performance will drop as there will be idling > >> > introduced between fsync thread and journalling thread. So that does > >> > not sound like a good idea either. > >> > > >> > Secondly, in presence of mixed workload (some other sync read happening) > >> > WRITES can get less bandwidth and sync workload much more. So by > >> > marking journal commits as WRITES you might increase the delay there > >> > in completion in presence of other sync workload. > >> > > >> > So Jan Kara's approach makes sense that if somebody is waiting on > >> > commit then make it WRITE_SYNC otherwise make it WRITE. Not sure why > >> > did it not work for you. Is it possible to run some traces and do > >> > more debugging that figure out what's happening. > >> Sorry for the long delay. > >> > >> Looks fedora enables ccache by default. While our kbuild test is on ext4 disk > >> but rootfs is on ext3 where ccache cache files live. Jan's patch only covers > >> ext4, maybe this is the reason. > >> I changed jbd to use WRITE for journal_commit_transaction. With the change and > >> Jan's patch, the test seems fine. > > Let me clarify the bug situation again. > > With the following scenarios, the regression is clear. > > 1, ccache_dir setup at rootfs that format is ext3 on /dev/sda1; 2, > > kbuild on /dev/sdb1 with ext4. > > but if we disable the ccache, only do kbuild on sdb1 with ext4. There is > > no regressions whenever with or without Jan's patch. > > So, problem focus on the ccache scenario, (from fedora 11, ccache is > > default setting). > > > > If we compare the vmstat output with or without ccache, there is too > > many write when ccache enabled. According the result, it should to do > > some tunning on ext3 fs. > Is ext3 configured with data ordered or writeback?
The ext3 on sda and ext4 on sdb are both used 'ordered' mounting mode.
> I think ccache might be performing fsyncs, and this is a bad workload > for ext3, especially in ordered mode. > It might be that my patch introduced a regression in ext3 fsync > performance, but I don't understand how reverting only the change in > jbd2 (that is the ext4 specific journaling daemon) could restore it. > The two partitions are on different disks, so each one should be > isolated from the I/O perspective (do they share a single > controller?).
No, sda/sdb use separated controller.
> The only interaction I see happens at the VM level, > since changing performance of any of the two changes the rate at which > pages can be cleaned. > > Corrado > > > > > > vmstat average output per 10 seconds, without ccache > > procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu----- > > r b swpd free buff cache si so bi bo in cs us sy id wa st > > 26.8 0.5 0.0 63930192.3 9677.0 96544.9 0.0 0.0 2486.9 337.9 17729.9 4496.4 17.5 2.5 79.8 0.2 0.0 > > > > vmstat average output per 10 seconds, with ccache > > procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu----- > > r b swpd free buff cache si so bi bo in cs us sy id wa st > > 2.4 40.7 0.0 64316231.0 17260.6 119533.8 0.0 0.0 2477.6 1493.1 8606.4 3565.2 2.5 1.1 83.0 13.5 0.0 > > > > > >> > >> Jan, > >> can you send a patch with similar change for ext3? So we can do more tests. > >> > >> Thanks, > >> Shaohua > > > > > > > > > > >
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