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Message-ID: <ce9626af-7f11-a556-1281-267b9f4422b4@codeaurora.org>
Date: Fri, 26 Jul 2019 14:36:29 +0530
From: Mukesh Ojha <mojha@...eaurora.org>
To: lkml <linux-kernel@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>,
Jiri Olsa <jolsa@...hat.com>, mingo@...hat.com, acme@...nel.org
Subject: Re: [PATCH RESEND V4 0/1] perf: Add CPU hotplug support for events
Hi All,
Can you please review this ?
Thanks,
Mukesh
On 6/24/2019 2:31 PM, Mukesh Ojha wrote:
> Friendly ping.
>
> On 6/18/2019 7:16 PM, Mukesh Ojha wrote:
>> The embedded world, specifically Android mobile SoCs, rely on CPU
>> hotplugs to manage power and thermal constraints. These hotplugs
>> can happen at a very rapid pace. Adjacently, they also relies on
>> many perf event counters for its management. Therefore, there is
>> a need to preserve these events across hotplugs.
>>
>> In such a scenario, a perf client (kernel or user-space) can create
>> events even when the CPU is offline. If the CPU comes online during
>> the lifetime of the event, the registered event can start counting
>> spontaneously. As an extension to this, the events' count can also
>> be preserved across CPU hotplugs. This takes the burden off of the
>> clients to monitor the state of the CPU.
>>
>> The tests were conducted on arm64 device.
>> /* CPU-1 is offline: Event created when CPU1 is offline */
>>
>> / # cat /sys/devices/system/cpu/cpu1/online
>> 1
>> / # echo 0 > /sys/devices/system/cpu/cpu1/online
>>
>> Test used for testing
>> #!/bin/sh
>>
>> chmod +x *
>>
>> # Count the cycles events on cpu-1 for every 200 ms
>> ./perf stat -e cycles -I 200 -C 1 &
>>
>> # Make the CPU-1 offline and online continuously
>> while true; do
>> sleep 2
>> echo 0 > /sys/devices/system/cpu/cpu1/online
>> sleep 2
>> echo 1 > /sys/devices/system/cpu/cpu1/online
>> done
>>
>> Results:
>> / # ./test.sh
>> # time counts unit events
>> 0.200145885 <not counted> cycles
>> 0.410115208 <not counted> cycles
>> 0.619922551 <not counted> cycles
>> 0.829904635 <not counted> cycles
>> 1.039751614 <not counted> cycles
>> 1.249547603 <not counted> cycles
>> 1.459228280 <not counted> cycles
>> 1.665606561 <not counted> cycles
>> 1.874981926 <not counted> cycles
>> 2.084297811 <not counted> cycles
>> 2.293471249 <not counted> cycles
>> 2.503231561 <not counted> cycles
>> 2.712993332 <not counted> cycles
>> 2.922744478 <not counted> cycles
>> 3.132502186 <not counted> cycles
>> 3.342255050 <not counted> cycles
>> 3.552010102 <not counted> cycles
>> 3.761760363 <not counted> cycles
>>
>> /* CPU-1 made online: Event started counting */
>>
>> 3.971459269 1925429 cycles
>> 4.181325206 19391145 cycles
>> 4.391074164 113894 cycles
>> 4.599130519 3150152 cycles
>> 4.805564737 487122 cycles
>> 5.015164581 247533 cycles
>> 5.224764529 103622 cycles
>> # time counts unit events
>> 5.434360831 238179 cycles
>> 5.645293799 238895 cycles
>> 5.854909320 367543 cycles
>> 6.064487966 2383428 cycles
>>
>> /* CPU-1 made offline: counting stopped
>>
>> 6.274289476 <not counted> cycles
>> 6.483493903 <not counted> cycles
>> 6.693202705 <not counted> cycles
>> 6.902956195 <not counted> cycles
>> 7.112714268 <not counted> cycles
>> 7.322465570 <not counted> cycles
>> 7.532222340 <not counted> cycles
>> 7.741975830 <not counted> cycles
>> 7.951686246 <not counted> cycles
>>
>> /* CPU-1 made online: Event started counting
>>
>> 8.161469892 22040750 cycles
>> 8.371219528 114977 cycles
>> 8.580979111 259952 cycles
>> 8.790757132 444661 cycles
>> 9.000559215 248512 cycles
>> 9.210385256 246590 cycles
>> 9.420187704 243819 cycles
>> 9.630052287 7102438 cycles
>> 9.839848225 337454 cycles
>> 10.049645048 644072 cycles
>> 10.259476246 1855410 cycles
>>
>> Mukesh Ojha (1):
>> perf: event preserve and create across cpu hotplug
>>
>> include/linux/perf_event.h | 1 +
>> kernel/events/core.c | 122
>> +++++++++++++++++++++++++++++----------------
>> 2 files changed, 79 insertions(+), 44 deletions(-)
>>
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