From: Jens Axboe <axboe@kernel.dk>
To: Bart Van Assche <bvanassche@acm.org>,
Matthew Wilcox <willy@infradead.org>,
Kaitao Cheng <pilgrimtao@gmail.com>
Cc: hch@lst.de, sth@linux.ibm.com, viro@zeniv.linux.org.uk,
clm@fb.com, jaegeuk@kernel.org, hch@infradead.org,
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damien.lemoal@wdc.com, ming.lei@redhat.com,
martin.petersen@oracle.com, satyat@google.com,
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asml.silence@gmail.com, ajay.joshi@wdc.com,
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hoeppner@linux.ibm.com, heiko.carstens@de.ibm.com,
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ocfs2-devel@oss.oracle.com, deepa.kernel@gmail.com
Subject: Re: [PATCH v2] blkdev: Replace blksize_bits() with ilog2()
Date: Fri, 29 May 2020 16:39:26 -0600 [thread overview]
Message-ID: <fe0fc36e-fa67-a6b9-cc7a-d86d3f21cf2c@kernel.dk> (raw)
In-Reply-To: <c7a5bbc4-ffc2-6a63-fed3-9874969afc31@acm.org>
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
prev parent reply other threads:[~2020-05-29 22:39 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-29 14:11 [PATCH v2] blkdev: Replace blksize_bits() with ilog2() Kaitao Cheng
2020-05-29 14:13 ` Jens Axboe
2020-06-01 7:22 ` Tao pilgrim
2020-06-01 8:44 ` Greg KH
2020-06-02 5:51 ` Christoph Hellwig
2020-06-02 6:13 ` Greg KH
2020-05-29 14:15 ` Christoph Hellwig
2020-05-29 20:27 ` Matthew Wilcox
2020-05-29 22:27 ` Bart Van Assche
2020-05-29 22:39 ` Jens Axboe [this message]
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