Re: [PATCH v2 00/15] Introduce threaded trace streaming for basic perf record operation

[Namhyung Kim]

Hi,

On Wed, Oct 28, 2020 at 1:02 AM Alexey Budankov
<alexey.budankov@xxxxxxxxxxxxxxx> wrote:
>
>
> On 27.10.2020 15:10, Jiri Olsa wrote:
> > On Mon, Oct 26, 2020 at 08:59:01PM +0300, Alexey Budankov wrote:
> >>
> >> On 24.10.2020 18:43, Jiri Olsa wrote:
> >>> On Wed, Oct 21, 2020 at 06:52:43PM +0300, Alexey Budankov wrote:
> >>>>
> >>>> Changes in v2:
> >>>> - explicitly added credit tags to patches 6/15 and 15/15,
> >>>>   additionally to cites [1], [2]
> >>>> - updated description of 3/15 to explicitly mention the reason
> >>>>   to open data directories in read access mode (e.g. for perf report)
> >>>> - implemented fix for compilation error of 2/15
> >>>> - explicitly elaborated on found issues to be resolved for
> >>>>   threaded AUX trace capture
> >>>>
> >>>> v1: https://lore.kernel.org/lkml/810f3a69-0004-9dff-a911-b7ff97220ae0@xxxxxxxxxxxxxxx/
> >>>>
> >>>> Patch set provides threaded trace streaming for base perf record
> >>>> operation. Provided streaming mode (--threads) mitigates profiling
> >>>> data losses and resolves scalability issues of serial and asynchronous
> >>>> (--aio) trace streaming modes on multicore server systems. The patch
> >>>> set is based on the prototype [1], [2] and the most closely relates
> >>>> to mode 3) "mode that creates thread for every monitored memory map".
> >>>
> >>> so what I liked about the previous code was that you could
> >>> configure how the threads would be created
> >>>
> >>> default --threads options created thread for each cpu like
> >>> in your change:
> >>>
> >>>   $ perf record -v --threads ...
> >>>   ...
> >>>   thread 0 monitor: 0 allowed: 0
> >>>   thread 1 monitor: 1 allowed: 1
> >>>   thread 2 monitor: 2 allowed: 2
> >>>   thread 3 monitor: 3 allowed: 3
> >>>   thread 4 monitor: 4 allowed: 4
> >>>   thread 5 monitor: 5 allowed: 5
> >>>   thread 6 monitor: 6 allowed: 6
> >>>   thread 7 monitor: 7 allowed: 7
> >>
> >> Yes, it is configurable in the prototype. Even though this patch set
> >> doesn't implement that parameters for --thread option, just because
> >> VTune doesn't have use cases for that yet, it has still been designed
> >> and implemented with that possible extension in mind so it could then
> >> be easily added on top of it.
> >
> > I'm not sure about vtune extensions, but if we are going to
> > have --threads option I believe we should make it configurable
> > at least to the extend descibed below
>
> It employs --threads mode only and there are no use cases
> observed so far beyond this mode. Do you have or see such
> use cases?

I don't know about vtune and other users, but it's an important
feature for better performance so I agree with Jiri's opinion to
make it flexible for the system requirement.

Thanks
Namhyung