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SubjectRe: [PATCH v2] blkdev: Replace blksize_bits() with ilog2()
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On 5/29/20 4:27 PM, Bart Van Assche wrote:
> On 2020-05-29 13:27, Matthew Wilcox wrote:
>> On Fri, May 29, 2020 at 10:11:00PM +0800, Kaitao Cheng wrote:
>>> There is a function named ilog2() exist which can replace blksize.
>>> The generated code will be shorter and more efficient on some
>>> architecture, such as arm64. And ilog2() can be optimized according
>>> to different architecture.
>>
>> We'd get the same benefit from a smaller patch with just:
>>
>> --- a/include/linux/blkdev.h
>> +++ b/include/linux/blkdev.h
>> @@ -1502,15 +1502,9 @@ static inline int blk_rq_aligned(struct request_queue *q, unsigned long addr,
>> return !(addr & alignment) && !(len & alignment);
>> }
>>
>> -/* assumes size > 256 */
>> static inline unsigned int blksize_bits(unsigned int size)
>> {
>> - unsigned int bits = 8;
>> - do {
>> - bits++;
>> - size >>= 1;
>> - } while (size > 256);
>> - return bits;
>> + return ilog2(size);
>> }
>>
>> static inline unsigned int block_size(struct block_device *bdev)
>
> Hi Matthew,
>
> I had suggested to change all blksize_bits() calls into ilog2() calls
> because I think that a single function to calculate the logarithm base 2
> is sufficient.

I think this should be a two-parter:

1) Use the inode blkbits where appropriate
2) Then do this change

I'm leaning towards just doing it in blksize_bits() instead of updating
every caller, unless there aren't that many left once we've gone
through patch 1.

--
Jens Axboe

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