linux-kernel - Re: Difficulties for compilation without extra optimisation

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Message-ID: <1b850dea-fdea-cc93-65fb-ba5e2082bcb9@users.sourceforge.net>
Date:   Mon, 4 Dec 2017 11:18:26 +0100
From:   SF Markus Elfring <elfring@...rs.sourceforge.net>
To:     Steven Rostedt <rostedt@...dmis.org>,
        kernel-janitors@...r.kernel.org
Cc:     linux-kselftest@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Trond Myklebust <trondmy@...marydata.com>
Subject: Re: Difficulties for compilation without extra optimisation

>> Will the compilation be a bit quicker when extra data processing
>> could be omitted?
> 
> Why would you care more about the time it takes to compile the kernel,
> than the time it takes for executing it?

I am also interested in the evolution of compilation time frames.


> Benchmarks are all about performance of a running kernel,

This is generally reasonable.


> nobody compares benchmarks of the time it takes to compile it.

I guess that the situation can be occasionally different there.


> Sure, we like to make the compile times quicker

Good to know …


> (heck, I wrote "make localmodconfig" for just that purpose),

Thanks.


> but we never favor compiler time over execution time.

I imagine that the speed expectations could be adjusted during software development,
couldn't they?


> In fact, if we can improve the execution performance by sacrificing compile time,
> we are happy to do that.

I guess that you would like to consider some constraints there.


>>> In fact, we do a lot of tricks to make sure that things work the way
>>> we expect it to, because we add broken code that only gets compiled out
>>> when gcc optimizes the code the way we expect it to be,
>>> and the kernel build will break otherwise.  
>>
>> * Can this goal be also achieved without the addition of “broken code”?
> 
> No.

Will any other contributors take another look?


>> * How do you think about to improve the error handling there?
> 
> It works just fine as is.

I hope that further software improvements can be achieved also for this use case.


> Errors that can be detected at build time are 100 times better
> than detecting them at execution time.

I agree to such a general view.

Will an other (or no) error message be more appropriate?

Regards,
Markus