On 11/12/18 8:27 AM, Andre Przywara wrote: > 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. Thank a lot for you reply. -- regards, -grygorii
