linux-kernel - Re: [PATCH] perf tools: Properly set the value of 'old' and 'head' in snapshot mode

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Date:   Sun, 9 Jun 2019 14:51:01 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        suzuki.poulose@....com, peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf tools: Properly set the value of 'old' and 'head'
 in snapshot mode

Hi Arnaldo,

On Fri, Jun 07, 2019 at 03:23:25PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Fri, Jun 07, 2019 at 02:44:25PM +0800, Leo Yan escreveu:
> > On Thu, Jun 06, 2019 at 05:10:56PM -0300, Arnaldo Carvalho de Melo wrote:
> > > Em Wed, Jun 05, 2019 at 10:16:33AM -0600, Mathieu Poirier escreveu:
> > > > This patch adds the necessay intelligence to properly compute the value
> > > > of 'old' and 'head' when operating in snapshot mode.  That way we can get
> > > > the latest information in the AUX buffer and be compatible with the
> > > > generic AUX ring buffer mechanic.
> > > 
> > > Leo, have you had the chance to test/review this one? Suzuki?
> > 
> > Sure.  I applied this patch on the perf/core branch (with latest
> > commit 3e4fbf36c1e3 'perf augmented_raw_syscalls: Move reading
> > filename to the loop') and passed testing with below steps:
> > 
> > # perf record -e cs_etm/@..._etr0/ -S -m,64 --per-thread ./sort &
> > [1] 19097
> > Bubble sorting array of 30000 elements
> > 
> > # kill -USR2 19097
> > # kill -USR2 19097
> > # kill -USR2 19097
> > [ perf record: Woken up 4 times to write data ]
> > [ perf record: Captured and wrote 0.753 MB perf.data ]
> > 
> > FWIW:
> > 
> > Tested-by: Leo Yan <leo.yan@...aro.org>
> 
> Thanks a lot, I've added your "Tester notes:" and also your Tested-by:.
> 
> As I don't have hardware (yet) to test these patches, tests by people
> who can test on real hardware is always super appreciated.

You are very welcome and it's my pleasure :)

> Any suggestions for a SBC that I could buy to be able to do so?

Below are several Arm development boards for referrence:

- DB410c [1]: This board is the first choice for myself, since this
  board provides Debian (and Fedora :) support and it supports the
  mainline kernel pretty well; the CoreSight also is well supported.

  This board is about 80 USD so the cost is not expensive; on the
  other hand, please note one cons is the SDRAM is only 1GB, this will
  be impossible if you build some big projects (e.g. LLVM/Clang and
  BCC); but it's sufficient for perf related development and
  verification.

- There have other several boards are in my mind:

  Raspberry Pi3 [2] and Hikey960 [3].

  Raspberry Pi3 misses some features in the mainline kernel [4] and it
  has not enabled CoreSight hardware tracing feature; Hikey960 also
  have some patches are out of the mainline kenrel.

  Except you have special requirement (e.g. you want to use the board to
  build LLVM/Clang/BCC with big DDR size, etc), these two boards can be
  secondary choices.

Please feel free let me know if you have questions for boards.

Thanks,
Leo Yan

[1] https://www.96boards.org/product/dragonboard410c/
[2] https://www.raspberrypi.org/products/raspberry-pi-3-model-b-plus/
[3] https://www.96boards.org/product/hikey960/
[4] https://www.raspberrypi.org/forums/viewtopic.php?t=236568