From: Tao pilgrim <pilgrimtao@gmail.com>
To: Jens Axboe <axboe@kernel.dk>
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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bvanassche@acm.org, ming.lei@redhat.com,
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asml.silence@gmail.com, ajay.joshi@wdc.com,
linux-kernel@vger.kernel.org,
Muchun Song <songmuchun@bytedance.com>,
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Subject: [Ocfs2-devel] [PATCH v2] blkdev: Replace blksize_bits() with ilog2()
Date: Mon, 1 Jun 2020 15:22:01 +0800 [thread overview]
Message-ID: <CAAWJmAZOQQQeNiTr48OSRRdO2pG+q4c=6gjT55CkWC5FN=HXmA@mail.gmail.com> (raw)
In-Reply-To: <c8412d98-0328-0976-e5f9-5beddc148a35@kernel.dk>
On Fri, May 29, 2020 at 10:13 PM Jens Axboe <axboe@kernel.dk> wrote:
>
> On 5/29/20 8:11 AM, 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.
>
> When you posted this last time, I said:
>
> "I like the simplification, but do you have any results to back up
> that claim? Is the generated code shorter? Runs faster?"
>
Hi Jens Axboe:
I did a test on ARM64.
unsigned int ckt_blksize(int size)
{
return blksize_bits(size);
}
unsigned int ckt_ilog2(int size)
{
return ilog2(size);
}
When I compiled it into assembly code, I got the following result,
0000000000000088 <ckt_blksize>:
88: 2a0003e8 mov w8, w0
8c: 321d03e0 orr w0, wzr, #0x8
90: 11000400 add w0, w0, #0x1
94: 7108051f cmp w8, #0x201
98: 53017d08 lsr w8, w8, #1
9c: 54ffffa8 b.hi 90 <ckt_blksize+0x8>
a0: d65f03c0 ret
a4: d503201f nop
00000000000000a8 <ckt_ilog2>:
a8: 320013e8 orr w8, wzr, #0x1f
ac: 5ac01009 clz w9, w0
b0: 4b090108 sub w8, w8, w9
b4: 7100001f cmp w0, #0x0
b8: 5a9f1100 csinv w0, w8, wzr, ne
bc: d65f03c0 ret
The generated code of ilog2 is shorter , and runs faster
> which you handily ignored, yet sending out a new version. I'm not
> going to apply this without justification, your commit message is
> handwavy at best.
>
Do I need to write the test content into commit message?
--
Yours,
Kaitao Cheng
next prev parent reply other threads:[~2020-06-01 7:22 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-29 14:11 [Ocfs2-devel] [PATCH v2] blkdev: Replace blksize_bits() with ilog2() Kaitao Cheng
2020-05-29 14:13 ` Jens Axboe
2020-06-01 7:22 ` Tao pilgrim [this message]
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
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