2016-02-29 12:18 GMT+01:00 tip-bot for Rik van Riel <tipbot@xxxxxxxxx>: > Commit-ID: ff9a9b4c4334b53b52ee9279f30bd5dd92ea9bdd > Gitweb: http://git.kernel.org/tip/ff9a9b4c4334b53b52ee9279f30bd5dd92ea9bdd > Author: Rik van Riel <riel@xxxxxxxxxx> > AuthorDate: Wed, 10 Feb 2016 20:08:27 -0500 > Committer: Ingo Molnar <mingo@xxxxxxxxxx> > 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@xxxxxxxxxx> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> > Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Cc: Mike Galbraith <efault@xxxxxx> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Cc: clark@xxxxxxxxxx > Cc: eric.dumazet@xxxxxxxxx > Cc: fweisbec@xxxxxxxxx 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. -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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