Messages in this thread | | | Date | Wed, 17 Jun 2015 11:11:01 +0800 | From | Yuyang Du <> | Subject | Re: [Resend PATCH v8 0/4] sched: Rewrite runnable load and utilization average tracking |
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Hi,
The sched_debug is informative, lets first give it some analysis.
The workload is 12 CPU hogging tasks (always runnable) and 1 dbench task doing fs ops (70% runnable) running at the same time.
Actually, these 13 tasks are in a task group /autogroup-9617, which has weight 1024.
So the 13 tasks at most can contribute to an average of 79 (=1024/13) to the group entity's load_avg:
cfs_rq[0]:/autogroup-9617 .se->load.weight : 2 .se->avg.load_avg : 0
cfs_rq[1]:/autogroup-9617 .se->load.weight : 80 .se->avg.load_avg : 79
cfs_rq[2]:/autogroup-9617 .se->load.weight : 79 .se->avg.load_avg : 78
cfs_rq[3]:/autogroup-9617 .se->load.weight : 80 .se->avg.load_avg : 81
cfs_rq[4]:/autogroup-9617 .se->load.weight : 80 .se->avg.load_avg : 79
cfs_rq[5]:/autogroup-9617 .se->load.weight : 79 .se->avg.load_avg : 77
cfs_rq[6]:/autogroup-9617 .se->load.weight : 159 .se->avg.load_avg : 156
cfs_rq[7]:/autogroup-9617 .se->load.weight : 64 (dbench) .se->avg.load_avg : 50
cfs_rq[8]:/autogroup-9617 .se->load.weight : 80 .se->avg.load_avg : 78
cfs_rq[9]:/autogroup-9617 .se->load.weight : 159 .se->avg.load_avg : 156
cfs_rq[10]:/autogroup-9617 .se->load.weight : 80 .se->avg.load_avg : 78
cfs_rq[11]:/autogroup-9617 .se->load.weight : 79 .se->avg.load_avg : 78
So this is very good runnable load avg accrued in the task group structure.
However, why the cpu0 is very underload?
The top cfs's load_avg is:
cfs_rq[0]: 754 cfs_rq[1]: 81 cfs_rq[2]: 85 cfs_rq[3]: 80 cfs_rq[4]: 142 cfs_rq[5]: 86 cfs_rq[6]: 159 cfs_rq[7]: 264 cfs_rq[8]: 79 cfs_rq[9]: 156 cfs_rq[10]: 78 cfs_rq[11]: 79
We see cfs_rq[0]'s load_avg is 754 even it is underloaded.
So the problem is:
1) The tasks in the workload have too small weight (only 79), because they share a task group.
2) Probably some "high" weight task even runnable a small time contribute "big" to cfs_rq's load_avg.
The patchset does what it wants to do:
1) very precise task group's load avg tracking from group to children tasks and from children tasks to group.
2) the combined runnable + blocked load_avg is effective, so the blocked avg made its impact.
I will try to figure out what makes the cfs_rq[0]'s 754 load_avg, but I also think that the tasks have so small weight that they are very easy to be fairly "imbalanced" ....
Peter, Ben, and others?
In addition, the util_avg sometimes is insanely big, I think I already found the problem.
Thanks, Yuyang
On Wed, Jun 17, 2015 at 01:15:01PM +0800, Boqun Feng wrote: > On Wed, Jun 17, 2015 at 11:06:50AM +0800, Boqun Feng wrote: > > Hi Yuyang, > > > > I've run the test as follow on tip/master without and with your > > patchset: > > > > On a 12-core system (Intel(R) Xeon(R) CPU X5690 @ 3.47GHz) > > run stress --cpu 12 > > run dbench 1 > > Sorry, I forget to say that `stress --cpu 12` and `dbench 1` are running > simultaneously. Thank Yuyang for reminding me that. > > Regards, > Boqun
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