linux-kernel - Re: [PATCH v1] perf tests: Run tests in parallel by default

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Date: Fri, 26 Apr 2024 16:06:29 +0100
From: James Clark <james.clark@....com>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>,
 Kan Liang <kan.liang@...ux.intel.com>, linux-perf-users@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] perf tests: Run tests in parallel by default



On 01/03/2024 17:47, Ian Rogers wrote:
> Switch from running tests sequentially to running in parallel by
> default. Change the opt-in '-p' or '--parallel' flag to '-S' or
> '--sequential'.
> 
> On an 8 core tigerlake an address sanitizer run time changes from:
> 326.54user 622.73system 6:59.91elapsed 226%CPU
> to:
> 973.02user 583.98system 3:01.17elapsed 859%CPU
> 
> So over twice as fast, saving 4 minutes.
> 

Apologies for not replying earlier before this was applied. But IMO this
isn't a good default. Tests that use things like exclusive PMUs
(Coresight for example) can never pass when run in parallel.

For CI it's arguable whether you'd want to trade stability for speed.
And for interactive sessions there was already the --parallel option
which was easy to add and have it in your bash history.

Now we've changed the default, any CI will need to be updated to add
--sequential if it wants all the tests to pass. Maybe we could do some
hack and gate it on interactive vs non interactive sessions, but that
might be getting too clever. (Or a "don't run in parallel" flag on
certain tests)


Thanks
James