linux-kernel - Re: arm64 + ARM64_64K

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Message-ID: <99e0b883-cf9f-2ab9-5003-d4506bfa461d@ti.com>
Date:   Thu, 8 Nov 2018 12:14:11 -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 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