[PATCH] snd_usb_caiaq: use likely()/unlikely()

[PATCH] snd_usb_caiaq: use likely()/unlikely()

[Daniel Mack]

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Use likely() and unlikely() in code which is called regularily.

Signed-off-by: Daniel Mack <daniel@caiaq.de>


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diff --git a/sound/usb/caiaq/caiaq-audio.c b/sound/usb/caiaq/caiaq-audio.c
index 24970a5..8cb417f 100644
--- a/sound/usb/caiaq/caiaq-audio.c
+++ b/sound/usb/caiaq/caiaq-audio.c
@@ -365,10 +365,10 @@ static void read_in_urb_mode2(struct snd_usb_caiaqdev *dev,
 
 				check_byte = MAKE_CHECKBYTE(dev, stream, i);
 				
-				if ((usb_buf[i] & 0x3f) != check_byte)
+				if (unlikely((usb_buf[i] & 0x3f) != check_byte))
 					dev->input_panic = 1;
 
-				if (usb_buf[i] & 0x80)
+				if (unlikely(usb_buf[i] & 0x80))
 					dev->output_panic = 1;
 			}
 		}
@@ -394,7 +394,7 @@ static void read_in_urb(struct snd_usb_caiaqdev *dev,
 			const struct urb *urb,
 			const struct usb_iso_packet_descriptor *iso)
 {
-	if (!dev->streaming)
+	if (unlikely(!dev->streaming))
 		return;
 
 	switch (dev->spec.data_alignment) {
@@ -406,7 +406,7 @@ static void read_in_urb(struct snd_usb_caiaqdev *dev,
 		break;
 	}
 
-	if (dev->input_panic || dev->output_panic) {
+	if (unlikely(dev->input_panic || dev->output_panic)) {
 		debug("streaming error detected %s %s\n", 
 				dev->input_panic ? "(input)" : "",
 				dev->output_panic ? "(output)" : "");
@@ -454,12 +454,12 @@ static void read_completed(struct urb *urb)
 	struct urb *out;
 	int frame, len, send_it = 0, outframe = 0;
 
-	if (urb->status || !info)
+	if (unlikely(urb->status || !info))
 		return;
 
 	dev = info->dev;
 
-	if (!dev->streaming)
+	if (unlikely(!dev->streaming))
 		return;
 
 	out = dev->data_urbs_out[info->index];
@@ -467,7 +467,7 @@ static void read_completed(struct urb *urb)
 	/* read the recently received packet and send back one which has
 	 * the same layout */
 	for (frame = 0; frame < FRAMES_PER_URB; frame++) {
-		if (urb->iso_frame_desc[frame].status)
+		if (unlikely(urb->iso_frame_desc[frame].status != 0))
 			continue;
 
 		len = urb->iso_frame_desc[outframe].actual_length;
@@ -488,7 +488,7 @@ static void read_completed(struct urb *urb)
 		outframe++;
 	}
 
-	if (send_it) {
+	if (likely(send_it)) {
 		out->number_of_packets = FRAMES_PER_URB;
 		out->transfer_flags = URB_ISO_ASAP;
 		usb_submit_urb(out, GFP_ATOMIC);
@@ -511,7 +511,7 @@ static void write_completed(struct urb *urb)
 	struct snd_usb_caiaq_cb_info *info = urb->context;
 	struct snd_usb_caiaqdev *dev = info->dev;
 
-	if (!dev->output_running) {
+	if (unlikely(!dev->output_running)) {
 		dev->output_running = 1;
 		wake_up(&dev->prepare_wait_queue);
 	}
diff --git a/sound/usb/caiaq/caiaq-device.c b/sound/usb/caiaq/caiaq-device.c
index e97d8b2..e1dbce5 100644
--- a/sound/usb/caiaq/caiaq-device.c
+++ b/sound/usb/caiaq/caiaq-device.c
@@ -42,7 +42,7 @@
 #endif
 
 MODULE_AUTHOR("Daniel Mack <daniel@caiaq.de>");
-MODULE_DESCRIPTION("caiaq USB audio, version 1.3.6");
+MODULE_DESCRIPTION("caiaq USB audio, version 1.3.7");
 MODULE_LICENSE("GPL");
 MODULE_SUPPORTED_DEVICE("{{Native Instruments, RigKontrol2},"
 			 "{Native Instruments, RigKontrol3},"
@@ -119,7 +119,7 @@ static void usb_ep1_command_reply_dispatch (struct urb* urb)
 	struct snd_usb_caiaqdev *dev = urb->context;
 	unsigned char *buf = urb->transfer_buffer;
 
-	if (urb->status || !dev) {
+	if (unlikely(urb->status || !dev)) {
 		log("received EP1 urb->status = %i\n", urb->status);
 		return;
 	}

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Re: [PATCH] snd_usb_caiaq: use likely()/unlikely()

[Adrian Bunk]

On Sat, Apr 12, 2008 at 10:13:31PM +0200, Daniel Mack wrote:
> Use likely() and unlikely() in code which is called regularily.
>...

Does it bring any measurable advantage?

Otherwise it's usually better to let the compiler decide how to optimize 
the code.

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

Re: [PATCH] snd_usb_caiaq: use likely()/unlikely()

[Daniel Mack]

Hi,

On Sat, Apr 12, 2008 at 11:21:27PM +0300, Adrian Bunk wrote:
> Does it bring any measurable advantage?
> 
> Otherwise it's usually better to let the compiler decide how to optimize 
> the code.

I didn't really measure, but how should the compiler know how likely a
certain condition in hardware state is? I thought, in such cases it's
generally a good idea to give the compiler some hints.

Daniel

Re: [PATCH] snd_usb_caiaq: use likely()/unlikely()

[Adrian Bunk]

On Sat, Apr 12, 2008 at 11:01:19PM +0200, Daniel Mack wrote:
> Hi,
> 
> On Sat, Apr 12, 2008 at 11:21:27PM +0300, Adrian Bunk wrote:
> > Does it bring any measurable advantage?
> > 
> > Otherwise it's usually better to let the compiler decide how to optimize 
> > the code.
> 
> I didn't really measure, but how should the compiler know how likely a
> certain condition in hardware state is? I thought, in such cases it's
> generally a good idea to give the compiler some hints.

gcc's heuristics often tends to guess better than programmers on how to 
optimize code since most people who think they know better how code 
should get optimized than the compiler do not actually know better...

And what you call "some hints" _forces_ the compiler to optimize for a 
certain condition (even if this e.g. results in bigger code or 
omitting some optimization).

Considering the lines of code and the number of contributors to the 
Linux kernel some annotations are always wrong and might cause more
harm than the correct ones gain.

If it's some hotpath and a current gcc does generate measurably faster 
code with a likely/unlikely it's justified, but otherwise it's better to 
leave gcc all freedom on how to optimize it.

> Daniel

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed