linux-kernel - Re: [PATCH v2] kallsyms: Fix sleeping function called from invalid context when CONFIG_KALLSYMS

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Message-ID: <Y702gW+5P5EepCkG@alley>
Date:   Tue, 10 Jan 2023 10:57:21 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     Zhen Lei <thunder.leizhen@...wei.com>,
        linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org,
        Anders Roxell <anders.roxell@...aro.org>
Subject: Re: [PATCH v2] kallsyms: Fix sleeping function called from invalid
 context when CONFIG_KALLSYMS_SELFTEST=y

On Mon 2023-01-09 16:12:53, Luis Chamberlain wrote:
> On Mon, Jan 09, 2023 at 02:40:27PM +0100, Petr Mladek wrote:
> > Why are try hardly comparable?
> > 
> > 1. The speed depends on the number of loaded modules
> >    and number of symbols. It highly depends on the configuration
> >    that was used to build the kernel.
> > 
> > 2. The test runs only once. As a result it is hard to judge
> >    how big is the noise.
> > 
> > 3. The noise might depend on the size and state of CPU caches.
> > 
> > 
> > I personally vote for removing this selftest!
> 
> Even so, just as with testing a filesystem with different types of
> configurations, at least testing a few configs helps and it's what
> we do. Then, if anyone ever wanted to try to increase performance
> on symbol lookup today they have no easy way to measure things. How
> would they go about comparing things performance without this selftest?

How many people cares about kallsyms performance, please?
Is it worth spending time one implementing and maintaining such a
selftest?

Yes, Zhen wanted to make it faster. But how likely will anyone else
try to make it even better? Do we need to spend time on this
in the meantime?


> This selftests helps generically with that *and* helps peg on to it any sanity
> checks you may wish to add to those APIs which we just don't want to do
> upstream.

>From my POV, it would be much more important to check if the API
works as expected. I mean that it gives the right results.

I am not sure that performance is that important to spend more time
on this one.

Also I am not sure if selftests are the right location for performance
tests. My understanding is that it is a framework for functional
testing. It is showing if the tests passed or not. But performance
tests do not give "pass or not" results.

Best Regards,
Petr