From: Takashi Iwai <tiwai@suse.de>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Jaroslav Kysela <perex@perex.cz>, Takashi Iwai <tiwai@suse.com>,
Mark Brown <broonie@kernel.org>,
linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-sound@vger.kernel.org,
Herve Codina <herve.codina@bootlin.com>
Subject: Re: [PATCH] ALSA: pcm: Rewrite recalculate_boundary() to avoid costly loop
Date: Mon, 09 Jun 2025 09:52:08 +0200 [thread overview]
Message-ID: <875xh58i8n.wl-tiwai@suse.de> (raw)
In-Reply-To: <4836e2cde653eebaf2709ebe30eec736bb8c67fd.1749202237.git.christophe.leroy@csgroup.eu>
On Fri, 06 Jun 2025 11:44:02 +0200,
Christophe Leroy wrote:
>
> 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>
Applied now to for-next branch. Thanks.
Takashi
prev parent reply other threads:[~2025-06-09 7:52 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-06-06 9:44 [PATCH] ALSA: pcm: Rewrite recalculate_boundary() to avoid costly loop Christophe Leroy
2025-06-09 7:52 ` Takashi Iwai [this message]
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