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From: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
To: Renjith Ponnappan <renjithponnapps@gmail.com>,
	Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	jolsa@kernel.org, linux-perf-users@vger.kernel.org
Subject: Re: Perf: Question about continuous background data collection
Date: Thu, 07 Oct 2021 06:17:29 -0300	[thread overview]
Message-ID: <383B1714-E2A5-4678-8348-5B2AA5BE0833@gmail.com> (raw)
In-Reply-To: <CAPNhM=YRUMw2VuHg3e5RH33UTCDG0guiqvCrfwb_kW_PkLvipw@mail.gmail.com>



On October 6, 2021 6:25:57 PM GMT-03:00, Renjith Ponnappan <renjithponnapps@gmail.com> wrote:
>Hello Arnaldo & Jiri,
>
>Thank you for your response.
>
>The perf daemon is the closest implementation for what I was looking for.
>Here we run perf in the back-ground, keep overwriting the samples being
>collected and use the SIGUSR2 to signal to the perf daemon to collect the
>perf data to a file. This fulfills the following requirements:
>
>   1. Run perf in the background to collect data
>   2. A method to signal perf to collect the samples for the current cycle.
>
>The last part of the requirement which  was:
>
>   1. The data-collection in step 2 above, rather than writing the data to
>   file store it in in-memory datastructure via pointer manipulation. We can
>   have a list of such samples stored in memory until the next step. This
>   helps free up the CPU cycles used by perf for writing to file for
>   applications.
>   2. A method to signal perf to dump all the collected samples into
>   separate files. This way the user can collect the stored samples when the
>   CPU is relatively free.
>
>Let me know whether we have support for storing samples as in-memory
>samples.

Have you looked at the URL I pointed to you?

https://www.spinics.net/lists/linux-perf-users/msg11455.html

More specifically, read about 'perf record --overwrite"

- Arnaldo
>
>Thanks in advance for your help!
>
>*cheers,*
>*Renjith*
>
>
>On Tue, Oct 5, 2021 at 12:00 AM Jiri Olsa <jolsa@redhat.com> wrote:
>
>> On Thu, Sep 30, 2021 at 10:39:21PM -0300, Arnaldo Carvalho de Melo wrote:
>> >
>> >
>> > On September 30, 2021 10:28:28 PM GMT-03:00, Renjith Ponnappan <
>> renjithponnapps@gmail.com> wrote:
>> > >Hello Peter/Ingo/Arnaldo,
>> > >
>> > >First of all, apologies if I bombarded you with an irrelevant question
>> in
>> > >your busy day and ignore this if the question is irrelevant.
>> > >
>> > >I had a question about continuous background data-collection with perf
>> and
>> > >hope you are the right person to answer this. If not, it would be great
>> if
>> > >you can redirect me to the right person.
>> > >
>> > >I am trying to build a CPU profiling system (on an embedded ARM Platform
>> > >with CPU/memory constraints) which has CPU Samples already collected
>> when
>> > >an application CPU starvation scenario occurs based on perf. The
>> > >implementation I am trying to use is:
>> > >
>> > >   1. Run perf in the background collecting samples for the entire
>> system
>> >
>> >
>> > This is already in perf:
>> >
>> > https://www.spinics.net/lists/linux-perf-users/msg11455.html
>> >
>> >
>> > Reply adding linux-perf-users@vger.kernel.org.
>> >
>> > - Arnaldo
>> >
>> >
>> > >   with a sleep period of 60 seconds
>> > >   2. When an application CPU starvation scenario occurs (detected and
>> > >   raised by applications) notify the collection process to store the
>> last
>> > >   perf collection as data to be analyzed offline.
>> > >
>> > >Have you come across such a scenario and any recommendations on this?
>> > >
>> > >The following are the two implementations I have on the above:
>> > >
>> > >   1. An external process which instructs perf to record the 60 seconds
>> by
>> > >   providing unique filenames each time. This approach was taking
>> around 40%
>> > >   CPU of a CPU core, everytime the perf record was getting written
>> (once for
>> > >   each 60 seconds cycle). This isn't okay as it could cause
>> aggravation of
>> > >   the CPU starvation situation.
>> > >   2. I tinkered with Perf Code to add the logic of looping and writing
>> the
>> > >   file incase of an event only. This did reduce the CPU to only the
>> case when
>> > >   an event was detected.
>>
>> hi,
>> and there's also perf daemon to run perf sessions on background:
>> https://lore.kernel.org/lkml/20210130234856.271282-19-jolsa@kernel.org/
>>
>> jirka
>>
>> > >
>> > >Would like to hear your opinion on whether approach 2 is the right way
>> here
>> > >and any suggestion/guidance you may have.
>> > >
>> > >Thanks in advance for this help!
>> > >
>> > >*cheers,*
>> > >*Renjith*
>> >
>>
>>

  parent reply	other threads:[~2021-10-07  9:19 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CAPNhM=aGeiKAVFDHWuP=GcAbgUz=JgWwtKfoRgmuxoG0gNfciQ@mail.gmail.com>
     [not found] ` <DA2A1D0F-1877-41D1-BC87-C0AE70D3E18C@gmail.com>
     [not found]   ` <YVv4B4syx36Co/0+@krava>
2021-10-06 21:29     ` Perf: Question about continuous background data collection Renjith Ponnappan
     [not found]     ` <CAPNhM=YRUMw2VuHg3e5RH33UTCDG0guiqvCrfwb_kW_PkLvipw@mail.gmail.com>
2021-10-07  9:17       ` Arnaldo Carvalho de Melo [this message]
2021-10-07 16:52         ` Jiri Olsa

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