Date: Sun, 11 Oct 2009 21:49:11 -0700 From: Steve Kargl <sgk@troutmask.apl.washington.edu> To: Alex R <alex@mailinglist.ahhyes.net> Cc: freebsd-current@freebsd.org Subject: Re: Scheduler weirdness Message-ID: <20091012044911.GA39479@troutmask.apl.washington.edu> In-Reply-To: <4AD2B203.8030405@mailinglist.ahhyes.net> References: <6729ad0409e449f8dbda69ecd8feb618.squirrel@webmail.lerctr.org> <20091012014846.GB38325@troutmask.apl.washington.edu> <fe073255a48a675c0a8ab5bb8c105e61.squirrel@webmail.lerctr.org> <20091012023912.GA38822@troutmask.apl.washington.edu> <4AD29937.2040004@mailinglist.ahhyes.net> <20091012043358.GA39364@troutmask.apl.washington.edu> <4AD2B203.8030405@mailinglist.ahhyes.net>
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On Mon, Oct 12, 2009 at 03:35:15PM +1100, Alex R wrote: > Steve Kargl wrote: > >On Mon, Oct 12, 2009 at 01:49:27PM +1100, Alex R wrote: > > > >>Steve Kargl wrote: > >> > >>>So, you have 4 cpus and 4 folding-at-home processes and you're > >>>trying to use the system with other apps? Switch to 4BSD. > >>> > >>> > >>> > >>I thought SCHED_ULE was meant to be a much better choice under an SMP > >>environment. Why are you suggesting he rebuild his kernel and use the > >>legacy scheduler? > >> > >> > > > >If you have N cpus and N+1 numerical intensitive applications, > >ULE may have poor performance compared to 4BSD. In OP's case, > >he has 4 cpus and 4 numerical intensity (?) applications. He, > >however, also is trying to use the system in some interactive > >way. > > > > > Ah ok. Is this just an accepted thing by the freebsd dev's or are they > trying to fix it? > Jeff appears to be extremely busy with other projects. He is aware of the problem, and I have set up my system to give him access when/if it is so desired. Here's the text of my last set of tests that I sent to him OK, I've manage to recreate the problem. User kargl launches a mpi job on node10 that creates two images on node20. This is command z in the top(1) info. 30 seconds later, user sgk lauches a mpi process on node10 that creates 8 images on node20. This is command rivmp in top(1) info. With 8 available cpus, this is a (slightly) oversubscribed node. For 4BSD, I see last pid: 1432; load averages: 8.68, 5.65, 2.82 up 0+01:52:14 17:07:22 40 processes: 11 running, 29 sleeping CPU: 100% user, 0.0% nice, 0.0% system, 0.0% interrupt, 0.0% idle Mem: 32M Active, 12M Inact, 203M Wired, 424K Cache, 29M Buf, 31G Free Swap: 4096M Total, 4096M Free PID USERNAME THR PRI NICE SIZE RES STATE C TIME CPU COMMAND 1428 sgk 1 124 0 81788K 5848K CPU3 6 1:13 78.81% rivmp 1431 sgk 1 124 0 81788K 5652K RUN 1 1:13 78.52% rivmp 1415 kargl 1 124 0 78780K 4668K CPU7 1 1:38 78.42% z 1414 kargl 1 124 0 78780K 4664K CPU0 0 1:37 77.25% z 1427 sgk 1 124 0 81788K 5852K CPU4 3 1:13 78.42% rivmp 1432 sgk 1 124 0 81788K 5652K CPU2 4 1:13 78.27% rivmp 1425 sgk 1 124 0 81788K 6004K CPU5 5 1:12 78.17% rivmp 1426 sgk 1 124 0 81788K 5832K RUN 6 1:13 78.03% rivmp 1429 sgk 1 124 0 81788K 5788K CPU6 7 1:12 77.98% rivmp 1430 sgk 1 124 0 81788K 5764K RUN 2 1:13 77.93% rivmp Notice, the accumulated times appear reasonable. At this point in the computations, rivmp is doing no communication between processes. z is the netpipe benchmark and is essentially sending messages between the two processes over the memory bus. For ULE, I see last pid: 1169; load averages: 7.56, 2.61, 1.02 up 0+00:03:15 17:13:01 40 processes: 11 running, 29 sleeping CPU: 100% user, 0.0% nice, 0.0% system, 0.0% interrupt, 0.0% idle Mem: 31M Active, 9392K Inact, 197M Wired, 248K Cache, 26M Buf, 31G Free Swap: 4096M Total, 4096M Free PID USERNAME THR PRI NICE SIZE RES STATE C TIME CPU COMMAND 1168 sgk 1 118 0 81788K 5472K CPU6 6 1:18 100.00% rivmp 1169 sgk 1 118 0 81788K 5416K CPU7 7 1:18 100.00% rivmp 1167 sgk 1 118 0 81788K 5496K CPU5 5 1:18 100.00% rivmp 1166 sgk 1 118 0 81788K 5564K RUN 4 1:18 100.00% rivmp 1151 kargl 1 118 0 78780K 4464K CPU3 3 1:48 99.27% z 1152 kargl 1 110 0 78780K 4464K CPU0 0 1:18 62.89% z 1164 sgk 1 113 0 81788K 5592K CPU1 1 0:55 80.76% rivmp 1165 sgk 1 110 0 81788K 5544K RUN 0 0:52 62.16% rivmp 1163 sgk 1 107 0 81788K 5624K RUN 2 0:40 50.68% rivmp 1162 sgk 1 107 0 81788K 5824K CPU2 2 0:39 50.49% rivmp In the above, processes 1162-1165 are clearly not receiving sufficient time slices to keep up with the other 4 rivmp images. From watching top at a 1 second interval, once the 4 rivmp hit 100% CPU, they stayed pinned to their cpu and stay at 100% CPU. It is also seen that processes 1152, 1165 and 1162, 1163 are stuck on cpus 0 and 2, respectively. -- Steve
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