Messages in this thread | ![/](/images/icornerl.gif) | | Date | Tue, 11 Jul 2023 08:22:12 +0530 | Subject | Re: [RFC PATCH 3/4] sched/fair: Calculate the scan depth for idle balance based on system utilization | From | K Prateek Nayak <> |
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Hello Chenyu,
Thank you for taking a look at the results.
On 7/10/2023 9:07 PM, Chen Yu wrote: > Hi Prateek, > > thanks for testing this patch, > On 2023-07-10 at 16:36:47 +0530, K Prateek Nayak wrote: >> Hello Chenyu, >> >> Thank you for sharing this extended version. Sharing the results from >> testing below. >> >> tl;dr >> >> - tbench, netperf and unixbench-spawn see an improvement with ILB_UTIL. >> >> - schbench (old) sees a regression in tail latency once system is heavily >> loaded. DeathStarBench and SPECjbb too see a small drop under those >> conditions. >> >> - Rest of the benchmark results do not vary much. >> >> > [...] >> I have a couple of theories: >> > Thanks for the insights, I agree the risk you mentioned below could impact the > performance. Some thoughts below: >> o Either new_idle_balance is failing to find an overloaded busy rq as a >> result of the limit. >> > If the system is overloaded, the ilb_util finds a relatively busy rq and pulls from it. > There could be no much difference between a relatively busy rq and the busiest one, > because all rqs are quite busy I suppose? >> o Or, there is a chain reaction where pulling from a loaded rq which is not >> the most loaded, will lead to more new_idle_balancing attempts which is >> degrading performance. > Yeah, it could be possible that the ilb_util finds a relatively busy rq, but the > imbalance is not high so ilb decides not pull from it. However the busiest > rq is still waiting for someone to help, and this could trigger idle load > balance more frequently.
Yes, I was thinking along the similar lines.
>> >> I'll go back and get some data to narrow down the cause. Meanwhile if >> there is any specific benchmark you would like me to run on the test >> system, please do let me know. >> > Another hints might be that, as Gautham and Peter suggested, we should apply ILB_UTIL > to non-Numa domains. In above patch all the domains has sd_share which could > bring negative impact when accessing/writing cross-node data. > Sorry I did not post the latest version with Numa domain excluded previously as > I was trying to create a protype to further speed up idle load balance by > reusing the statistic suggested by Peter. I will send them out once it is stable.
Sure. I'll keep an eye out for the next version :)
> > [..snip..] >
-- Thanks and Regards, Prateek
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