[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Notes on stubdoms and latency on ARM
Hi, On 17/07/17 10:25, George Dunlap wrote: On 07/12/2017 07:14 AM, Dario Faggioli wrote:On Fri, 2017-07-07 at 14:12 -0700, Stefano Stabellini wrote:On Fri, 7 Jul 2017, Volodymyr Babchuk wrote:Since you are using Credit, can you try to disable context switch rate limiting?Yep. You are right. In the environment described above (Case 2) I now get much better results: real 1.85 user 0.00 sys 1.85From 113 to 1.85 -- WOW! Obviously I am no scheduler expert, but shouldn't we advertise a bit better a scheduler configuration option that makes things _one hundred times faster_ ?!So, to be fair, so far, we've bitten this hard by this only on artificially constructed test cases, where either some extreme assumption were made (e.g., that all the vCPUs except one always run at 100% load) or pinning was used in a weird and suboptimal way. And there are workload where it has been verified that it helps making performance better (poor SpecVIRT results without it was the main motivation having it upstream, and on by default). That being said, I personally have never liked rate-limiting, it always looked to me like the wrong solution.In fact, I *think* the only reason it may have been introduced is that there was a bug in the credit2 code at the time such that it always had a single runqueue no matter what your actual pcpu topology was. FWIW, we don't yet parse the pCPU topology on ARM. AFAIU, we always tell Xen each CPU is in its own core. Will it have some implications in the scheduler? Cheers, -- Julien Grall _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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