linux-kernel - Re: MD-RAID: Use seq_putc() in three status functions?

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Message-ID: <05d0cade-7922-9d8a-a974-34b2cc9150fb@suse.de>
Date:   Mon, 17 Oct 2016 17:33:31 +0200
From:   Hannes Reinecke <hare@...e.de>
To:     SF Markus Elfring <elfring@...rs.sourceforge.net>,
        linux-raid@...r.kernel.org
Cc:     Bernd Petrovitsch <bernd@...rovitsch.priv.at>,
        Christoph Hellwig <hch@....de>,
        Guoqing Jiang <gqjiang@...e.com>, Jens Axboe <axboe@...com>,
        Joe Perches <coupons@...ches.com>,
        Mike Christie <mchristi@...hat.com>,
        Neil Brown <neilb@...e.com>, Shaohua Li <shli@...nel.org>,
        Tomasz Majchrzak <tomasz.majchrzak@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org, kbuild-all@...org,
        ltp@...ts.linux.it
Subject: Re: MD-RAID: Use seq_putc() in three status functions?

On 10/17/2016 04:30 PM, SF Markus Elfring wrote:
>>> Am I the only software developer so far who would dare to reconsider
>>> implementation details from three status functions?
>>>
>> No.
>
> Thanks for this kind of promising feedback.
>
>
>> But we're waiting for you showing is that it is an improvement.
>
> Can this aspect also be clarified to some degree from a logical point of view?
>
I sincerely doubt that.
We've discussed the logical implications already, and failed to come to 
a consensus. So we need some proof (as in: on this architecture I'm 
seeing this and that performance improvements).
Which you have to deliver.

> * Would you really like to know under which circumstances data processing
>   will be faster for a single character instead of using a string pointer
>   and corresponding two characters?
>
It's not a problem of the interface, it's a problem of the resulting 
code (ie assembler output). We can discuss all we like, if the compiler 
decides to throw in an optimisation none of the arguments even apply.

> * Do you care for a changed memory allocation characteristic?
>
> * Will it occasionally be useful to avoid the storage for another string literal?
>
Occasionally: yes.
In this particular case: hardly.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@...e.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)