linux-kernel - Re: arm64 + ARM64_64K

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Date:   Fri, 9 Nov 2018 13:15:47 -0600
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC:     <linux-rt-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Linux ARM Mailing List <linux-arm-kernel@...ts.infradead.org>
Subject: Re: arm64 + ARM64_64K_PAGES=y



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 (  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 ..."

-- 
regards,
-grygorii