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Date: Fri, 29 May 2020 16:39:26 -0600 From: Jens Axboe <axboe@...nel.dk> To: Bart Van Assche <bvanassche@....org>, Matthew Wilcox <willy@...radead.org>, Kaitao Cheng <pilgrimtao@...il.com> Cc: hch@....de, sth@...ux.ibm.com, viro@...iv.linux.org.uk, clm@...com, jaegeuk@...nel.org, hch@...radead.org, mark@...heh.com, dhowells@...hat.com, balbi@...nel.org, damien.lemoal@....com, ming.lei@...hat.com, martin.petersen@...cle.com, satyat@...gle.com, chaitanya.kulkarni@....com, houtao1@...wei.com, asml.silence@...il.com, ajay.joshi@....com, linux-kernel@...r.kernel.org, songmuchun@...edance.com, hoeppner@...ux.ibm.com, heiko.carstens@...ibm.com, gor@...ux.ibm.com, borntraeger@...ibm.com, linux-s390@...r.kernel.org, sagi@...mberg.me, linux-nvme@...ts.infradead.org, gregkh@...uxfoundation.org, linux-usb@...r.kernel.org, josef@...icpanda.com, dsterba@...e.com, linux-btrfs@...r.kernel.org, chao@...nel.org, linux-f2fs-devel@...ts.sourceforge.net, darrick.wong@...cle.com, linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org, jlbec@...lplan.org, joseph.qi@...ux.alibaba.com, ocfs2-devel@....oracle.com, deepa.kernel@...il.com Subject: Re: [PATCH v2] blkdev: Replace blksize_bits() with ilog2() 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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