Subject: Re: MD-RAID: Use seq_putc() in three status functions?
To: Hannes Reinecke <hare@suse.de>, linux-raid@vger.kernel.org
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Cc: Christoph Hellwig <hch@lst.de>, Guoqing Jiang <gqjiang@suse.com>,
        Jens Axboe <axboe@fb.com>, Joe Perches <coupons@perches.com>,
        Mike Christie <mchristi@redhat.com>, Neil Brown <neilb@suse.com>,
        Shaohua Li <shli@kernel.org>,
        Tomasz Majchrzak <tomasz.majchrzak@intel.com>,
        LKML <linux-kernel@vger.kernel.org>, kernel-janitors@vger.kernel.org,
        kbuild-all@01.org, ltp@lists.linux.it
From: SF Markus Elfring <elfring@users.sourceforge.net>
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Date: Mon, 17 Oct 2016 13:10:18 +0200
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>> * Is a string pointer often longer than a byte?
>>
> Always.

I have got doubts for this specific information.


> (Which up to now I thought was basic programming knowledge...)

By the way:
Run time environments still exist where the size of a pointer can be also
just one byte, don't they?


>> How many results would we like to clarify from various hardware
>> and software combinations?
>>
> See above. At the moment _any_ test result from your side would do.

I imagine that another single result might not be representative.
How many lessons from test statistics will usually be also relevant here?


>> How important are the mentioned functions for you within the Linux
>> programming interface so far?
>>
> Not very. The interface is only used in a slow path, and the execution
> time doesn't affect I/O performance in any way.

Thanks for another interesting information.


>>> Case in point: with your patch the x86_64 compiler generates nearly
>>> identical code for driver/md/raid1.c, but with one instruction _more_
>>> after your patch has been applied.
>>
>> Which software versions and command parameters did you try out
>> for this information (from an unspecified run time environment)?
>>
> # gcc --version
> gcc (SUSE Linux) 4.8.5

Thanks for this detail.

* Did you choose any special optimisation settings for your quick check?

* Will any compilation results matter if "optimisation" would be
  switched off there?


> I'm still waiting from results from your side.

Would any other software developers or testers dare to add related information?

Regards,
Markus