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

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Date:   Tue, 10 Jan 2023 20:20:16 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Petr Mladek <pmladek@...e.com>,
        Luis Chamberlain <mcgrof@...nel.org>
CC:     <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 2023/1/10 17:57, Petr Mladek wrote:
> 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.

I think both of you have a point. In the absence of a better way to
improve it, perhaps deleting the performance test is the best option now.
OK, I'll do this first.

> 
> Best Regards,
> Petr
> .
> 

-- 
Regards,
  Zhen Lei