Messages in this thread | | | Date | Tue, 6 Jan 2009 20:37:09 +0530 | From | Vaidyanathan Srinivasan <> | Subject | Re: [PATCH v7 0/8] Tunable sched_mc_power_savings=n |
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* Mike Galbraith <efault@gmx.de> [2009-01-06 10:31:37]:
> On Mon, 2009-01-05 at 16:19 +0100, Mike Galbraith wrote: > > On Mon, 2009-01-05 at 07:37 +0100, Mike Galbraith wrote: > > > > > I'll rummage around. > > > > Seems to be about the only thing it could be, load balancing inflicting > > injury on very sensitive mysql+oltp pairs. > > BTW, I verified this. Reverting all load-balancing changes fully > restored mysql+oltp peak, and brought mid-range throughput to the same > level as sched_mc=2 except at the log-jam end. (haven't looked at > vmark, though I'd expect it to be hurting a bit too, it's affinity > sensitive as well) > > I expected sched_mc=2 to help an nfs mount kbuild, and it did, quite a > bit. I first tried an nfs4 mount, but after a while, the odd ipv6 80% > idle problem came back, so I reverted to nfs3. Full built time there > went from 4m25s to 4m2s. A nice improvement. > > I haven't noticed anything on the interactivity front. > > Personally, I'd go for sched_mc=2 as default. I value the fork/exec > load much more than sensitive benchmarks, though what hurts mysql+oltp > will certainly hurt others as well. We have a bit of conflict between > keeping CPUs busy and affinity cost. Something to work on.
Hi Mike,
Thanks for the detailed benchmark reports. Glad to hear that sched_mc=2 is helping in most scenarios. Though we would be tempted to make it default, I would still like to default to zero in order to provide base line performance. I would expect end users to flip the settings to sched_mc=2 if it helps their workload in terms of performance and/or power savings.
The fact that sched_mc=2 provide performance and/or power saving benefits is a good justification to include the new code and tunable.
The benefits from the sched_mc=2 settings vary widely based on workload and system configuration. Hence in my opinion, I would not want to change the default to 2 at this time until more wide spread use of the tunable under various workloads and system configurations.
--Vaidy
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