6.15-stable review patch. If anyone has any objections, please let me know.
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From: Christophe Leroy christophe.leroy@csgroup.eu
[ Upstream commit 92f59aeb13252265c20e7aef1379a8080c57e0a2 ]
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... Signed-off-by: Takashi Iwai tiwai@suse.de Signed-off-by: Sasha Levin sashal@kernel.org --- sound/core/pcm_native.c | 19 +++++++++++++++---- 1 file changed, 15 insertions(+), 4 deletions(-)
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c index 853ac5bb33ff..ecb71bf1859d 100644 --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -24,6 +24,7 @@ #include <sound/minors.h> #include <linux/uio.h> #include <linux/delay.h> +#include <linux/bitops.h>
#include "pcm_local.h"
@@ -3130,13 +3131,23 @@ struct snd_pcm_sync_ptr32 { static snd_pcm_uframes_t recalculate_boundary(struct snd_pcm_runtime *runtime) { snd_pcm_uframes_t boundary; + snd_pcm_uframes_t border; + int order;
if (! runtime->buffer_size) return 0; - boundary = runtime->buffer_size; - while (boundary * 2 <= 0x7fffffffUL - runtime->buffer_size) - boundary *= 2; - return boundary; + + border = 0x7fffffffUL - runtime->buffer_size; + if (runtime->buffer_size > border) + return runtime->buffer_size; + + order = __fls(border) - __fls(runtime->buffer_size); + boundary = runtime->buffer_size << order; + + if (boundary <= border) + return boundary; + else + return boundary / 2; }
static int snd_pcm_ioctl_sync_ptr_compat(struct snd_pcm_substream *substream,