Messages in this thread | | | Subject | Re: hackbench regression since 2.6.25-rc | From | "Zhang, Yanmin" <> | Date | Fri, 14 Mar 2008 08:50:19 +0800 |
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On Thu, 2008-03-13 at 10:12 -0700, Greg KH wrote: > On Thu, Mar 13, 2008 at 09:19:21AM -0700, Randy Dunlap wrote: > > On Thu, 13 Mar 2008 08:14:13 -0700 Greg KH wrote: > > > > > On Thu, Mar 13, 2008 at 03:46:57PM +0800, Zhang, Yanmin wrote: > > > > Comparing with 2.6.24, on my 16-core tigerton, hackbench process mode has about > > > > 40% regression with 2.6.25-rc1, and more than 20% regression with kernel > > > > 2.6.25-rc4, because rc4 includes the reverting patch of scheduler load balance. > > > > > > > > Command to start it. > > > > #hackbench 100 process 2000 > > > > I ran it for 3 times and sum the values. > > > > > > > > I tried to investiagte it by bisect. > > > > Kernel up to tag 0f4dafc0563c6c49e17fe14b3f5f356e4c4b8806 has the 20% regression. > > > > Kernel up to tag 6e90aa972dda8ef86155eefcdbdc8d34165b9f39 hasn't regression. > > > > > > > > Any bisect between above 2 tags cause kernel hang. I tried to checkout to a point between > > > > these 2 tags for many times manually and kernel always paniced. > > > > > > Where is the kernel panicing? The changeset right after the last one > > > above: bc87d2fe7a1190f1c257af8a91fc490b1ee35954, is a change to efivars, > > > are you using that in your .config? > > > > > > > All patches between the 2 tags are on kobject restructure. I guess such restructure > > > > creates more cache miss on the 16-core tigerton. > > > > > > Nothing should be creating kobjects on a normal load like this, so a > > > regression seems very odd. Unless the /sys/kernel/uids/ stuff is > > > triggering this? > > > > > > Do you have a link to where I can get hackbench (google seems to find > > > lots of reports with it, but not the source itself), so I can test to > > > see if we are accidentally creating kobjects with this load? > > > > The version that I see referenced most often (unscientifically :) > > is somewhere under people.redhat.com/mingo/, like so: > > http://people.redhat.com/mingo/cfs-scheduler/tools/hackbench.c > > Great, thanks for the link. > > In using that version, I do not see any kobjects being created at all > when running the program. So I don't see how a kobject change could > have caused any slowdown. > > Yanmin, is the above link the version you are using? Yes.
> > Hm, running with "hackbench 100 process 2000" seems to lock up my > laptop, maybe I shouldn't run 4000 tasks at once on such a memory > starved machine... The issue doesn't exist on my 8-core stoakley and on tulsa. So I don't think you could reproduce it on laptop.
>From the oprofile data, perhaps we need dig into SLUB firstly.
-yanmin
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