Re: arm64 + ARM64_64K_PAGES=y

[Grygorii Strashko]

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%
>>>
>>> cyclictest -n -m -Sp98 -q -D2m with CONFIG_ARM64_64K_PAGES=y
>>>
>>>
>>> T: 0 (Â 772) P:98 I:1000 C: 120000 Min:ÂÂÂÂÂ 7 Act:ÂÂ 13 Avg:ÂÂ 10 Max:ÂÂÂÂÂ 85
>>> T: 1 (Â 773) P:98 I:1500 C:Â 79998 Min:ÂÂÂÂÂ 7 Act:ÂÂ 13 Avg:ÂÂ 10 Max:ÂÂÂÂÂ 71
>>> T: 2 (Â 774) P:98 I:2000 C:Â 59997 Min:ÂÂÂÂÂ 7 Act:ÂÂ 11 Avg:ÂÂ 11 Max:ÂÂÂÂÂ 64
>>> T: 3 (Â 775) P:98 I:2500 C:Â 47996 Min:ÂÂÂÂÂ 7 Act:ÂÂ 14 Avg:ÂÂ 12 Max:ÂÂÂÂÂ 66
>>>
>>>
>>> cyclictest -n -m -Sp98 -q -D2m with CONFIG_ARM64_64K_PAGES=n
>>>
>>>
>>> T: 0 (Â 697) P:98 I:1000 C: 120000 Min:ÂÂÂÂÂ 7 Act:ÂÂ 10 Avg:ÂÂÂ 9 Max:ÂÂÂÂÂ 38
>>> T: 1 (Â 698) P:98 I:1500 C:Â 79987 Min:ÂÂÂÂÂ 7 Act:ÂÂ 10 Avg:ÂÂ 10 Max:ÂÂÂÂÂ 32
>>> T: 2 (Â 699) P:98 I:2000 C:Â 59981 Min:ÂÂÂÂÂ 7 Act:ÂÂ 14 Avg:ÂÂ 11 Max:ÂÂÂÂÂ 46
>>> T: 3 (Â 700) P:98 I:2500 C:Â 47977 Min:ÂÂÂÂÂ 6 Act:ÂÂ 11 Avg:ÂÂ 10 Max:ÂÂÂÂÂ 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 ..."

-- 
regards,
-grygorii