Messages in this thread | | | From | Andy Lutomirski <> | Date | Sun, 3 May 2015 11:24:20 -0700 | Subject | Re: [PATCH 3/3] context_tracking,x86: remove extraneous irq disable & enable from context tracking on syscall entry |
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On Sun, May 3, 2015 at 10:30 AM, Rik van Riel <riel@redhat.com> wrote: > On 05/03/2015 09:23 AM, Mike Galbraith wrote: > >> Below are v4.1-rc1-172-g6c3c1eb3c35e + patches measurements. >> >> 100M * stat() on isolated cpu >> >> NO_HZ_FULL off inactive housekeeper nohz_full >> real 0m14.266s 0m14.367s 0m20.427s 0m27.921s >> user 0m1.756s 0m1.553s 0m1.976s 0m10.447s >> sys 0m12.508s 0m12.769s 0m18.400s 0m17.464s >> (real) 1.000 1.007 1.431 1.957 >> 1.000 1.000 >> >> real 0m20.423s 0m27.930s +rik 1,2 >> user 0m2.072s 0m10.450s >> sys 0m18.304s 0m17.471s >> vs off 1.431 1.957 >> vs prev 1.000 1.000 >> >> real 0m20.256s 0m27.803s +paolo 1,2 (2 missing prototypes) >> user 0m1.884s 0m10.551s >> sys 0m18.353s 0m17.242s >> vs off 1.419 1.948 >> vs prev .991 .995 >> >> real 0m19.122s 0m26.946s +rik 3 >> user 0m1.896s 0m10.292s >> sys 0m17.198s 0m16.644s >> vs off 1.340 1.888 >> vs prev .944 .969 > > I'm convinced. > > Time to try the remote sampling of CPU use statistics, and > lighten up the RCU overhead of context tracking. >
I don't understand the remote sampling proposal. Isn't the whole point of full nohz to avoid periodically interrupting a busy CPU? If what you have in mind is sending IPIs, then that's just as bad, right?
If, on the other hand, you're just going to remotely sample the in-memory context, that sounds good.
--Andy
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