linux-kernel - Re: sparc: bpf_jit: Move four assignments in bpf_jit

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Date:   Sun, 4 Sep 2016 08:28:13 +0200
From:   SF Markus Elfring <elfring@...rs.sourceforge.net>
To:     Julian Calaby <julian.calaby@...il.com>
Cc:     sparclinux <sparclinux@...r.kernel.org>,
        Adam Buchbinder <adam.buchbinder@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Rabin Vincent <rabin@....in>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors <kernel-janitors@...r.kernel.org>,
        Julia Lawall <julia.lawall@...6.fr>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: sparc: bpf_jit: Move four assignments in bpf_jit_compile()

>> Which test environments would you find acceptable for further clarification?
> 
> Compiling it on GCC for Sparc, obviously.

Are there any more configuration details to consider?

>>> I must also point out that these sorts of optimisations are things the
>>> compiler does automatically when compiling this code.
>>
>> Do you take this detail for granted?
> 
> I trust that the GCC developers have done their work well.

Will any more compiler implementations matter here?

Do you like software which can run better by default also without application
of special compilation parameters?

> I'm looking for some glimmer of usefullness in this patch. I'm not seeing any.

Thanks for your honest feedback.

>> Should we avoid to compare software things similar to "apples" and "oranges"
>> (while these fruits can make more fun)?   ;-)
> 
> Write a benchmark that exercises this function. Measure the time it
> took without this change, measure the time it took with this change,
> is there a difference.

Is an accepted test system already available for the purpose that every commit
would be checked in the way automatically you expect here?

> You cannot expect people to take you seriously if you're proposing
> performance changes without any actual ability or interest in
> producing performance related data to go along with them.

I suggested small changes which I found "logical".

> You're essentially saying "I think doing things this way is better"

Yes …

> and providing _nothing_ else.

You might be looking for more information than I can practically give you
at the moment.

> I think that things are perfectly fine the way they are.

I have got an other impression for "perfection" in this software module.
I found an implementation detail for further considerations.

> Convince me with data or something else.

I imagine that the "else" can become harder than you find reasonable.

> Did someone do this to some other driver and you're applying the same fix elsewhere?

Is a similar software development discussion still running for other modules?

> You are the only person proposing changes like these ones as you are

I am picking special software improvement opportunities up.

> (as far as I know) the only person who thinks they have any value.

I can accept that the value of specific changes will usually be categorised
as lower than updates that you prefer so far.

Regards,
Markus