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92f59aeb13
At the time being recalculate_boundary() is implemented with a
loop which shows up as costly in a perf profile, as depicted by
the annotate below:
0.00 : c057e934: 3d 40 7f ff lis r10,32767
0.03 : c057e938: 61 4a ff ff ori r10,r10,65535
0.21 : c057e93c: 7d 49 50 50 subf r10,r9,r10
5.39 : c057e940: 7d 3c 4b 78 mr r28,r9
2.11 : c057e944: 55 29 08 3c slwi r9,r9,1
3.04 : c057e948: 7c 09 50 40 cmplw r9,r10
2.47 : c057e94c: 40 81 ff f4 ble c057e940 <snd_pcm_ioctl+0xee0>
Total: 13.2% on that simple loop.
But what the loop does is to multiply the boundary by 2 until it is
over the wanted border. This can be avoided by using fls() to get the
boundary value order and shift it by the appropriate number of bits at
once.
This change provides the following profile:
0.04 : c057f6e8: 3d 20 7f ff lis r9,32767
0.02 : c057f6ec: 61 29 ff ff ori r9,r9,65535
0.34 : c057f6f0: 7d 5a 48 50 subf r10,r26,r9
0.23 : c057f6f4: 7c 1a 50 40 cmplw r26,r10
0.02 : c057f6f8: 41 81 00 20 bgt c057f718 <snd_pcm_ioctl+0xf08>
0.26 : c057f6fc: 7f 47 00 34 cntlzw r7,r26
0.09 : c057f700: 7d 48 00 34 cntlzw r8,r10
0.22 : c057f704: 7d 08 38 50 subf r8,r8,r7
0.04 : c057f708: 7f 5a 40 30 slw r26,r26,r8
0.35 : c057f70c: 7c 0a d0 40 cmplw r10,r26
0.13 : c057f710: 40 80 05 f8 bge c057fd08 <snd_pcm_ioctl+0x14f8>
0.00 : c057f714: 57 5a f8 7e srwi r26,r26,1
Total: 1.7% with that loopless alternative.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://patch.msgid.link/4836e2cde653eebaf2709ebe30eec736bb8c67fd.1749202237.git.christophe.leroy@csgroup.eu
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.