linux-kernel - Re: [PATCH 1/2] perf: Add closing sibling events' file descriptors

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Message-ID: <87364t1plf.fsf@ashishki-desk.ger.corp.intel.com>
Date:   Tue, 11 Aug 2020 12:47:24 +0300
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     peterz@...radead.org, Arnaldo Carvalho de Melo <acme@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Jiri Olsa <jolsa@...nel.org>, alexey.budankov@...ux.intel.com,
        adrian.hunter@...el.com, alexander.shishkin@...ux.intel.com
Subject: Re: [PATCH 1/2] perf: Add closing sibling events' file descriptors

Andi Kleen <ak@...ux.intel.com> writes:

>> It didn't. I can't figure out what to charge on the locked memory, as
>> all that memory is in kernel-side objects. It also needs to make sense
>
> I don't see how that makes a difference for the count. It just account
> bytes. Can you elaborate?

Right, but which bytes? One byte per event? That's
arbitrary. sizeof(struct perf_event)? Then, probably also sizeof(struct
perf_event_context).

>> as iirc the default MLOCK_LIMIT is quite low, you'd hit it sooner than
>> the file descriptor limit.
>
> For a single process? 

The above two structs add up to 2288 bytes on my local build. Given the
default RLIMIT_MEMLOCK of 64k, that's 28 events. As opposed to ~1k
events if we keep using the RLIMIT_NOFILE. Unless I'm missing your
point.

Regards,
--
Alex