Re: [sched,rcu] 9234566d3a3: +1.6% will-it-scale.scalability, +1302.6% time.involuntary_context_switches

[Jet Chen]

On 04/22/2014 09:59 AM, Paul E. McKenney wrote:
> On Mon, Apr 21, 2014 at 02:28:21PM +0800, Jet Chen wrote:
> > Hi Paul,
> >
> > we noticed the below changes on
> > git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git torture.2014.04.18a
> > commit 9234566d3a36c0aead8852e3c2ca94cd8ebfe219 ("sched,rcu: Make cond_resched() report RCU quiescent states")
>
> My impression of these statistics is that this commit results in huge
> numbers of additional context switches and interrupts, but has a slightly
> positive effect on performance and a larger negative effect on
> scalability.
>
> Is this a reasonable interpretation?
Yes, you're right.


> 							Thanx, Paul
>
> > Comparison 1 - parent commit of 9234566d3a36c0aead8852e3c2ca94cd8ebfe219 vs 9234566d3a36c0aead8852e3c2ca94cd8ebfe219
> >
> > e119454e74a852f  9234566d3a36c0aead8852e3c
> > ---------------  -------------------------
> >      1035948 ~ 0%      +1.6%    1052990 ~ 0%  TOTAL will-it-scale.per_thread_ops
> >      1271322 ~ 0%      +1.8%    1294004 ~ 0%  TOTAL will-it-scale.per_process_ops
> >         0.63 ~ 0%      -5.2%       0.60 ~ 0%  TOTAL will-it-scale.scalability
> >        22470 ~ 2%   +1302.6%     315168 ~ 2%  TOTAL time.involuntary_context_switches
> >        84265 ~ 5%   +1047.1%     966581 ~ 1%  TOTAL interrupts.IWI
> >         1828 ~44%    +189.6%       5295 ~13%  TOTAL time.voluntary_context_switches
> >         5337 ~ 1%     +82.1%       9720 ~ 1%  TOTAL vmstat.system.cs
> >       118599 ~ 0%     -30.4%      82545 ~ 0%  TOTAL interrupts.0:IO-APIC-edge.timer
> >       224021 ~ 4%     +34.7%     301858 ~ 2%  TOTAL interrupts.RES
> >        25148 ~ 0%      +7.0%      26917 ~ 0%  TOTAL vmstat.system.in
> >      7063439 ~ 0%      -5.2%    6694536 ~ 0%  TOTAL interrupts.LOC
> >       188866 ~ 0%      -3.1%     183008 ~ 0%  TOTAL interrupts.NMI
> >       188866 ~ 0%      -3.1%     183008 ~ 0%  TOTAL interrupts.PMI
> >         3720 ~ 0%      -1.5%       3665 ~ 0%  TOTAL time.system_time
> >         1215 ~ 0%      -1.4%       1198 ~ 0%  TOTAL time.percent_of_cpu_this_job_got
> >
> >
> > Comparison 2 - b84c4e08143c98dad4b4d139f08db0b98b0d3ec4 vs 9234566d3a36c0aead8852e3c2ca94cd8ebfe219
> >
> > Fengguang has reported stats changes about b84c4e08143c98dad4b4d139f08db0b98b0d3ec4 to you days ago.
> > git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2014.04.14a
> > commit b84c4e08143c98dad4b4d139f08db0b98b0d3ec4 ("sched,rcu: Make cond_resched() report RCU quiescent states")
> >
> > Let's have a compare here.
> >
> > b84c4e08143c98d  9234566d3a36c0aead8852e3c
> > ---------------  -------------------------
> >       809309 ~ 0%      -2.6%     788400 ~ 0%  TOTAL will-it-scale.per_process_ops
> >         0.61 ~ 0%      -1.9%       0.60 ~ 0%  TOTAL will-it-scale.scalability
> >       434080 ~ 0%      -1.5%     427643 ~ 0%  TOTAL will-it-scale.per_thread_ops
> >            4 ~11%  +1.2e+05%       5249 ~ 2%  TOTAL interrupts.IWI
> >          607 ~ 7%     +28.0%        778 ~14%  TOTAL interrupts.47:PCI-MSI-edge.eth0
> >        12349 ~ 2%     -14.6%      10548 ~ 1%  TOTAL interrupts.0:IO-APIC-edge.timer
> >         3078 ~ 3%     +20.9%       3722 ~ 6%  TOTAL interrupts.RES
> >
> >
> > Comparison 3 - parent commit of b84c4e08143c98dad4b4d139f08db0b98b0d3ec4 vs b84c4e08143c98dad4b4d139f08db0b98b0d3ec4
> >
> > Duplicated with Fengguang's report. Help you to see these info in a page :)
> >
> > ad86a04266f9b49  b84c4e08143c98dad4b4d139f
> > ---------------  -------------------------
> >       676264 ~ 0%      +3.3%     698461 ~ 0%  TOTAL will-it-scale.per_thread_ops
> >      1174547 ~ 0%      +3.0%    1209307 ~ 0%  TOTAL will-it-scale.per_process_ops
> >         1.67 ~ 0%      -2.3%       1.63 ~ 0%  TOTAL will-it-scale.scalability
> >        10522 ~ 2%    +921.2%     107463 ~ 1%  TOTAL time.involuntary_context_switches
> >        77671 ~ 3%     +67.0%     129688 ~ 3%  TOTAL interrupts.RES
> >        99502 ~ 0%     -27.8%      71813 ~ 0%  TOTAL interrupts.0:IO-APIC-edge.timer
> >         2554 ~ 0%     +49.1%       3809 ~ 1%  TOTAL vmstat.system.cs
> >        11524 ~ 0%      -2.3%      11259 ~ 0%  TOTAL vmstat.system.in
> >          213 ~ 0%      -4.3%        204 ~ 0%  TOTAL time.system_time
> >           74 ~ 0%      -4.1%         71 ~ 0%  TOTAL time.percent_of_cpu_this_job_got
> >      3495099 ~ 0%      -3.1%    3387173 ~ 0%  TOTAL interrupts.LOC
> >
> >
> >
> >
> > Thanks,
> > Jet
>
> > ./runtest.py open2 32 1 4 6 8
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