Re: [PATCH 2/2] sched,time: call __acct_update_integrals once a jiffy
From: Rik van Riel
Date: Fri Jan 29 2016 - 17:43:35 EST
On 01/29/2016 05:23 PM, riel@xxxxxxxxxx wrote:
> From: Rik van Riel <riel@xxxxxxxxxx>
> This speeds up
... ok, that changelog got truncated :(
Here is the full version:
Because __acct_update_integrals does nothing unless the time
interval in question exceeds a jiffy, there is no real reason
to call it more than once a jiffy from the syscall, irq, and
guest entry & exit paths.
If tasks get rescheduled frequently, the scheduler will still
update their time statistics normally.
However, longer running tasks with frequent syscall, irq,
or guest entry & exit see a difference with this patch.
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 patch, 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 + both patches 2.3 seconds
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