Re: [RFC/RFT][PATCH v6] cpuidle: New timer events oriented governor for tickless systems

Rafael J. Wysocki
2018-12-03T23:38:14Z

On Saturday, December 1, 2018 3:18:24 PM CET Giovanni Gherdovich wrote:
> On Fri, 2018-11-23 at 11:35 +0100, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >

[cut]

> >
> > [snip]
>
> [NOTE: the tables in this message are quite wide. If this doesn't get to you
> properly formatted you can read a copy of this message at the URL
> https://beta.suse.com/private/ggherdovich/teo-eval/teo-v6-eval.html ]
>
> All performance concerns manifested in v5 are wiped out by v6. Not only v6
> improves over v5, but is even better than the baseline (menu) in most
> cases. The optimizations in v6 paid off!

This is very encouraging, thank you!

> The overview of the analysis for v5, from the message
> https://lore.kernel.org/lkml/1541877001.17878.5.camel@suse.cz , was:
>
> > The quick summary is:
> >
> > ---> sockperf on loopback over UDP, mode "throughput":
> > this had a 12% regression in v2 on 48x-HASWELL-NUMA, which is completely
> > recovered in v3 and v5. Good stuff.
> >
> > ---> dbench on xfs:
> > this was down 16% in v2 on 48x-HASWELL-NUMA. On v5 we're at a 10%
> > regression. Slight improvement. What's really hurting here is the single
> > client scenario.
> >
> > ---> netperf-udp on loopback:
> > had 6% regression on v2 on 8x-SKYLAKE-UMA, which is the same as what
> > happens in v5.
> >
> > ---> tbench on loopback:
> > was down 10% in v2 on 8x-SKYLAKE-UMA, now slightly worse in v5 with a 12%
> > regression. As in dbench, it's at low number of clients that the results
> > are worst. Note that this machine is different from the one that has the
> > dbench regression.
>
> now the situation is overturned:
>
> ---> sockperf on loopback over UDP, mode "throughput":
> No new problems from 48x-HASWELL-NUMA, which stays put at the level of
> the baseline. OTOH 80x-BROADWELL-NUMA and 8x-SKYLAKE-UMA improve over the
> baseline of 8% and 10% respectively.

Good.

> ---> dbench on xfs:
> 48x-HASWELL-NUMA rebounds from the previous 10% degradation and it's now
> at 0, i.e. the baseline level. The 1-client case, responsible for the
> previous overall degradation (I average results from different number of
> clients), went from -40% to -20% and is compensated in my table by
> improvements with 4, 8, 16 and 32 clients (table below).
>
> ---> netperf-udp on loopback:
> 8x-SKYLAKE-UMA now shows a 9% improvement over baseline.
> 80x-BROADWELL-NUMA, previously similar to baseline, now improves 7%.

Good.

> ---> tbench on loopback:
> Impressive change of color for 8x-SKYLAKE-UMA, from 12% regression in v5
> to 7% improvement in v6. The problematic 1- and 2-clients cases went from
> -25% and -33% to +13% and +10% respectively.

Awesome. :-)

> Details below.
>
> Runs are compared against v4.18 with the Menu governor. I know v4.18 is a
> little old now but that's where I measured my baseline. My machine pool didn't
> change:
>
> * single socket E3-1240 v5 (Skylake 8 cores, which I'll call 8x-SKYLAKE-UMA)
> * two sockets E5-2698 v4 (Broadwell 80 cores, 80x-BROADWELL-NUMA from here onwards)
> * two sockets E5-2670 v3 (Haswell 48 cores, 48x-HASWELL-NUMA from here onwards)
>

[cut]

>
>
> PREVIOUSLY REGRESSING BENCHMARKS: OVERVIEW
> ==========================================
>
> * sockperf on loopback over UDP, mode "throughput"
> * global-dhp__network-sockperf-unbound
> 48x-HASWELL-NUMA fixed since v2, the others greatly improved in v6.
>
> teo-v1 teo-v2 teo-v3 teo-v5 teo-v6
> -------------------------------------------------------------------------------
> 8x-SKYLAKE-UMA 1% worse 1% worse 1% worse 1% worse 10% better
> 80x-BROADWELL-NUMA 3% better 2% better 5% better 3% worse 8% better
> 48x-HASWELL-NUMA 4% better 12% worse no change no change no change
>
> * dbench on xfs
> * global-dhp__io-dbench4-async-xfs
> 48x-HASWELL-NUMA is fixed wrt v5 and earlier versions.
>
> teo-v1 teo-v2 teo-v3 teo-v5 teo-v6
> -------------------------------------------------------------------------------
> 8x-SKYLAKE-UMA 3% better 4% better 6% better 4% better 5% better
> 80x-BROADWELL-NUMA no change no change 1% worse 3% worse 2% better
> 48x-HASWELL-NUMA 6% worse 16% worse 8% worse 10% worse no change
>
> * netperf on loopback over UDP
> * global-dhp__network-netperf-unbound
> 8x-SKYLAKE-UMA fixed.
>
> teo-v1 teo-v2 teo-v3 teo-v5 teo-v6
> -------------------------------------------------------------------------------
> 8x-SKYLAKE-UMA no change 6% worse 4% worse 6% worse 9% better
> 80x-BROADWELL-NUMA 1% worse 4% worse no change no change 7% better
> 48x-HASWELL-NUMA 3% better 5% worse 7% worse 5% worse no change
>
> * tbench on loopback
> * global-dhp__network-tbench
> Measurable improvements across all machines, especially 8x-SKYLAKE-UMA.
>
> teo-v1 teo-v2 teo-v3 teo-v5 teo-v6
> -------------------------------------------------------------------------------
> 8x-SKYLAKE-UMA 1% worse 10% worse 11% worse 12% worse 7% better
> 80x-BROADWELL-NUMA 1% worse 1% worse no cahnge 1% worse 4% better
> 48x-HASWELL-NUMA 1% worse 2% worse 1% worse 1% worse 5% better

So I'm really happy with this, but I'm afraid that the v6 may be a little too
agressive. Also my testing (with the "low" and "high" counters introduced by
https://patchwork.kernel.org/patch/10709463/) shows that it generally is
a bit worse than menu with respect to matching the observed idle duration
as it tends to prefer shallower states. This appears to be in agreement with
the Doug's results too.

For this reason, I'm going to send a v7 with a few changes relative to v6 to
make it somewhat more energy-efficient. If it turns out to be much worse than
the v6 performance-wise, though, the v6 may be a winner. :-)

Thanks,
Rafael