Messages in this thread | | | Date | Mon, 29 Feb 2016 16:31:56 +0100 | Subject | Re: [tip:sched/core] sched, time: Switch VIRT_CPU_ACCOUNTING_GEN to jiffy granularity | From | Frederic Weisbecker <> |
| |
2016-02-29 12:18 GMT+01:00 tip-bot for Rik van Riel <tipbot@zytor.com>: > Commit-ID: ff9a9b4c4334b53b52ee9279f30bd5dd92ea9bdd > Gitweb: http://git.kernel.org/tip/ff9a9b4c4334b53b52ee9279f30bd5dd92ea9bdd > Author: Rik van Riel <riel@redhat.com> > AuthorDate: Wed, 10 Feb 2016 20:08:27 -0500 > Committer: Ingo Molnar <mingo@kernel.org> > CommitDate: Mon, 29 Feb 2016 09:53:10 +0100 > > sched, time: Switch VIRT_CPU_ACCOUNTING_GEN to jiffy granularity > > When profiling syscall overhead on nohz-full kernels, > after removing __acct_update_integrals() from the profile, > native_sched_clock() remains as the top CPU user. This can be > reduced by moving VIRT_CPU_ACCOUNTING_GEN to jiffy granularity. > > This will reduce timing accuracy on nohz_full CPUs to jiffy > based sampling, just like on normal CPUs. It results in > totally removing native_sched_clock from the profile, and > significantly speeding up the syscall entry and exit path, > as well as irq entry and exit, and KVM guest entry & exit. > > Additionally, only call the more expensive functions (and > advance the seqlock) when jiffies actually changed. > > This code relies on another CPU advancing jiffies when the > system is busy. On a nohz_full system, this is done by a > housekeeping CPU. > > A microbenchmark calling an invalid syscall number 10 million > times in a row speeds up an additional 30% over the numbers > with just the previous patches, for a total speedup of about > 40% over 4.4 and 4.5-rc1. > > Run times for the microbenchmark: > > 4.4 3.8 seconds > 4.5-rc1 3.7 seconds > 4.5-rc1 + first patch 3.3 seconds > 4.5-rc1 + first 3 patches 3.1 seconds > 4.5-rc1 + all patches 2.3 seconds > > A non-NOHZ_FULL cpu (not the housekeeping CPU): > > all kernels 1.86 seconds > > Signed-off-by: Rik van Riel <riel@redhat.com> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > Reviewed-by: Thomas Gleixner <tglx@linutronix.de> > Cc: Linus Torvalds <torvalds@linux-foundation.org> > Cc: Mike Galbraith <efault@gmx.de> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: clark@redhat.com > Cc: eric.dumazet@gmail.com > Cc: fweisbec@gmail.com
It seems the tip bot doesn't parse correctly the Cc tags as I wasn't cc'ed on this commit.
Also I wish I had a chance to test and ack this patch before it got applied. I guess I should have told I was in vacation for the last weeks.
I'm going to run it through some tests.
Thanks.
| |