Messages in this thread | | | Subject | Re: [PATCH] x86/xen: Add "xen_timer_slop" command line option | From | Boris Ostrovsky <> | Date | Mon, 25 Mar 2019 09:43:20 -0400 |
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On 3/25/19 8:05 AM, luca abeni wrote: > Hi all, > > On Sat, 23 Mar 2019 11:41:51 +0100 > luca abeni <luca.abeni@santannapisa.it> wrote: > [...] >>>> Is there any data that shows effects of using this new parameter? >>>> >>> Yes, I've done some research and experiments on this. I did it >>> together with a friend, which I'm Cc-ing, as I'm not sure we're >>> ready/capable to share the results, yet (Luca?). >> I think we can easily share the experimental data (cyclictest output >> and plots). >> >> Moreover, we can share the scripts and tools for running the >> experiments (so, everyone can easily reproduce the numbers by simply >> typing "make" and waiting for some time :) >> >> >> I'll try to package the results and the scripts/tools this evening, >> and I'll send them. > Sorry for the delay. I put some quick results here: > http://retis.santannapisa.it/luca/XenTimers/ > (there also is a link to the scripts to be used for reproducing the > results). The latencies have been measured by running cyclictest in the > guest (see the scripts for details). > > The picture shows the latencies measured with an unpatched guest kernel > and with a guest kernel having TIMER_SLOP set to 1000 (arbitrary small > value :). > All the experiments have been performed booting the hypervisor with a > small timer_slop (the hypervisor's one) value. So, they show that > decreasing the hypervisor's timer_slop is not enough to measure low > latencies with cyclictest.
I have a couple of questions: * Does it make sense to make this a tunable for other clockevent devices as well? * This patch adjusts min value. Could max value (ever) need a similar adjustment?
-boris
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