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Subject: Re: [PATCH v2 2/2] blk-mq: Add a polling specific stats function
To: Stephen Bates <sbates@raithlin.com>
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From: Jens Axboe <axboe@kernel.dk>
Message-ID: <bb76465b-d708-f5df-e2ec-c99d052e9b27@kernel.dk>
Date: Fri, 7 Apr 2017 08:01:45 -0600
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On 04/07/2017 06:11 AM, Stephen  Bates wrote:
> On 2017-04-05, 7:14 PM, "Jens Axboe" <axboe@kernel.dk> wrote:
> 
>> Why not just have 8 buckets, and make it:
>>
>> 	bucket = ddir + ilog2(bytes) - 9;
>>
>> and cap it at MAX_BUCKET (8) and put all those above into the top
>> bucket.
> 
> Thanks. However, that equation does not differentiate between
> direction and size. Instead we can use
> 
> bucket = ddir + 2*(ilog2(bytes) - 9);

It would be cleaner to just embed the fact that we have 2 sets of
identical buckets, and return 

	bucket = ilog2(bytes) - 9;

and have poll_stat be indexed by:

	->poll_stat[ddir][bucket];

instead.

-- 
Jens Axboe