Re: arm64 + ARM64_64K_PAGES=y

[Grygorii Strashko]

On 11/8/18 6:00 AM, Sebastian Andrzej Siewior wrote:
> On 2018-11-06 15:34:55 [-0600], Grygorii Strashko wrote:
> > Hi All,
> Hi,
>
> > Do anybody tried to use ARM64 RT with 76K pages enabled?
>
> 75 would be an off by one but this :)

Ops 8-). at least subj is correct.

> > My attempt shows that enabling  CONFIG_ARM64_64K_PAGES=y increases latencies by ~30%
> >
> > cyclictest -n -m -Sp98 -q -D2m with CONFIG_ARM64_64K_PAGES=y
> >
> >
> > T: 0 (  772) P:98 I:1000 C: 120000 Min:      7 Act:   13 Avg:   10 Max:      85
> > T: 1 (  773) P:98 I:1500 C:  79998 Min:      7 Act:   13 Avg:   10 Max:      71
> > T: 2 (  774) P:98 I:2000 C:  59997 Min:      7 Act:   11 Avg:   11 Max:      64
> > T: 3 (  775) P:98 I:2500 C:  47996 Min:      7 Act:   14 Avg:   12 Max:      66
> >
> >
> > cyclictest -n -m -Sp98 -q -D2m with CONFIG_ARM64_64K_PAGES=n
> >
> >
> > T: 0 (  697) P:98 I:1000 C: 120000 Min:      7 Act:   10 Avg:    9 Max:      38
> > T: 1 (  698) P:98 I:1500 C:  79987 Min:      7 Act:   10 Avg:   10 Max:      32
> > T: 2 (  699) P:98 I:2000 C:  59981 Min:      7 Act:   14 Avg:   11 Max:      46
> > T: 3 (  700) P:98 I:2500 C:  47977 Min:      6 Act:   11 Avg:   10 Max:      45
>
> So this is an idle system?

Yes (in general) - it's collected with systemd, so some daemons are active.

> The Kconfig help says "faster TLB lookup". Interesting.
> Are the 16k pages in between (latency wise) by any chance?

I'll try it.


--
regards,
-grygorii