On Thu, Apr 17, 2014 at 06:55:03AM -0700, Paul E. McKenney wrote:
> On Thu, Apr 17, 2014 at 12:03:53PM +0800, Fengguang Wu wrote:
> > Hi Paul,
> >
> > FYI, this improves will-it-scale/open1 throughput.
>
> Cool! Not a planned benefit, but I will take it. ;-)
>
> > 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")
>
> But how should I read the data below? I see lots of positive percentages
> and lots of negative percentages for the delta, and all near zero for
> standard deviation. Is the overall improvement an average of these or
> some such? What is being measured?
There are a lot of things being measured, which are shown after each
"TOTAL". For example, to get an overview of the report:
grep "TOTAL" this_email
563496 ~ 0% +3.1% 581059 ~ 0% TOTAL will-it-scale.per_thread_ops
756894 ~ 0% +2.8% 778452 ~ 0% TOTAL will-it-scale.per_process_ops
0.57 ~ 0% -2.7% 0.55 ~ 0% TOTAL will-it-scale.scalability
346764 ~ 2% -74.0% 90164 ~ 1% TOTAL
slabinfo.kmalloc-256.active_objs
10837 ~ 2% -73.9% 2824 ~ 1% TOTAL
slabinfo.kmalloc-256.active_slabs
10837 ~ 2% -73.9% 2824 ~ 1% TOTAL
slabinfo.kmalloc-256.num_slabs
346821 ~ 2% -73.9% 90393 ~ 1% TOTAL slabinfo.kmalloc-256.num_objs
105961 ~ 1% -63.0% 39153 ~ 1% TOTAL meminfo.SUnreclaim
26432 ~ 1% -62.9% 9814 ~ 1% TOTAL
proc-vmstat.nr_slab_unreclaimable
87318 ~ 0% +130.0% 200809 ~ 0% TOTAL softirqs.RCU
140354 ~ 1% -47.6% 73490 ~ 0% TOTAL meminfo.Slab
77391 ~ 1% -46.7% 41235 ~ 2% TOTAL cpuidle.C6-NHM.usage
38368 ~ 2% -37.6% 23954 ~ 2% TOTAL softirqs.SCHED
1.24 ~ 4% -35.4% 0.80 ~ 3% TOTAL
perf-profile.cpu-cycles.do_notify_resume.int_signal.close
1.43 ~ 4% +41.9% 2.03 ~ 4% TOTAL
perf-profile.cpu-cycles.rcu_process_callbacks.__do_softirq.irq_exit.smp_apic_timer_in
rupt.apic_timer_interrupt
1.27 ~ 3% -30.0% 0.89 ~ 6% TOTAL
perf-profile.cpu-cycles.setup_object.isra.46.new_slab.__slab_alloc.kmem_cache_alloc.g
empty_filp
1.54 ~ 7% +35.6% 2.09 ~ 8% TOTAL
perf-profile.cpu-cycles.kmem_cache_alloc.getname_flags.getname.do_sys_open.sys_open
4.21 ~ 2% -29.1% 2.98 ~ 3% TOTAL
perf-profile.cpu-cycles.link_path_walk.path_openat.do_filp_open.do_sys_open.sys_open
1.37 ~ 4% -23.1% 1.05 ~ 7% TOTAL
perf-profile.cpu-cycles.__d_lookup_rcu.lookup_fast.link_path_walk.path_openat.do_filp
en
0.88 ~17% +29.1% 1.14 ~ 9% TOTAL
perf-profile.cpu-cycles.path_init.path_openat.do_filp_open.do_sys_open.sys_open
0.67 ~16% +33.6% 0.90 ~10% TOTAL
perf-profile.cpu-cycles.restore_sigcontext.sys_rt_sigreturn.stub_rt_sigreturn.raise
3.19 ~ 1% +17.4% 3.74 ~ 5% TOTAL
perf-profile.cpu-cycles.file_free_rcu.rcu_process_callbacks.__do_softirq.irq_exit.smp
ic_timer_interrupt
4329 ~ 7% +15.2% 4986 ~ 5% TOTAL
slabinfo.vm_area_struct.active_objs
2536 ~ 1% -75.8% 614 ~ 9% TOTAL
time.involuntary_context_switches
32593 ~ 1% -62.1% 12349 ~ 2% TOTAL
interrupts.0:IO-APIC-edge.timer
6934 ~ 9% +86.2% 12908 ~ 7% TOTAL interrupts.RES
490 ~ 1% -37.3% 307 ~ 1% TOTAL vmstat.system.cs
1639 ~ 0% -8.8% 1495 ~ 0% TOTAL vmstat.system.in
819681 ~ 0% -3.7% 789527 ~ 0% TOTAL interrupts.LOC
> > Legend:
> > ~XX% - stddev percent
> > [+-]XX% - change percent
> >
> >
> > time.involuntary_context_switches
> >
> > 3500
> > ++------------------------------------------------------------------+
> > | .*..
> > |
> > 3000 ++ .*. *..*.. .*..*.. .*..
> > |
> > *..*..*..*. *. *
> > |
> > | *..*.. .*.. .*..*
> > |
> > 2500 ++ *..*. *..*.
> > |
> > |
> > |
> > 2000 ++
> > |
> > |
> > |
> > 1500 ++
> > |
> > |
> > |
> > |
> > |
> > 1000 ++
> > |
> > | O O O O O O O O
> > O
> > 500
> > O+-O-----------O--O--O--O--------O-O--O--O--O--O--------O-----O--O--+
> >
> >
> > [*] bisect-good sample
> > [O] bisect-bad sample
>
> So the good case increases involuntary context switches, but helps something
> else? Or does the benefit stem from increased involuntary context switches
> and thus less time spinning or some such?
In bisect POV, branch BASE is good and HEAD is bad. Which has nothing
to do with the improvement/regression in performance POV.
Here the HEAD(bisect bad) commit has less involuntary_context_switches
which indicates an improvement over BASE. It does look like close to
the root cause of improved will-it-scale throughput.
Thanks,
Fengguang
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