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

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

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?

							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
> 
>