On Fri, 9 Nov 2018 13:15:47 -0600 Grygorii Strashko <grygorii.strashko@xxxxxx> wrote: Hi, > On 11/8/18 12:14 PM, Grygorii Strashko wrote: > > > > > > 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% That's not really surprising. Performance on systems using a bigger page size granules might have some trade-offs (bigger memory overhead, worse cache utilization), so 64K pages might not be really great for your particular workload. You would probably need a real performance analysis (using perf, for instance) to pinpoint TLB misses as your bottleneck. > >>> cyclictest -n -m -Sp98 -q -D2m with =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. > > no i'll not, at least not fast. with 16k pages enabled I can't boot > TI 4.14 kernel > - 4.14.71-rt44. > No msg in log, just "Starting kernel ..." You need a core that actually supports 16K pages (supporting certain page size granules is architecturally optional). >From the Arm Ltd. cores it's Cortex-A73, A75 or A55, possibly other newer ones as well. Cortex-A53, A57 and A72 do not support 16k pages. Cheers, Andre.
