Re: [alsa-devel] [PATCH] ALSA: add support for disabling period irq

On Mon, 1 Nov 2010, Pierre-Louis Bossart wrote:

Merged and cleaned patch based on earlier patches posted on alsa-devel by Clemens Ladisch clemens@ladisch.de and Pierre-Louis Bossart pierre-louis.bossart@intel.com

This patch disables period interrupts which are not needed when the application relies on a system timer to wake-up and refill the ring buffer. The behavior of the driver is left unchanged, and interrupts are only disabled if the application requests this configuration. The behavior in case of underruns is slightly different, instead of being detected during the period interrupts the underruns are detected when the application calls snd_pcm_update_avail, which in turns forces a refresh of the hw pointer and shows the buffer is empty.

More specifically this patch makes a lot of sense when PulseAudio relies on timer-based scheduling to access audio devices such as HDAudio or Intel SST. Disabling interrupts removes two unwanted wake-ups due to period elapsed events in low-power playback modes. It also simplifies PulseAudio voice modules used for speech calls.

To quote Lennart "This patch looks very interesting and desirable. This is something have long been waiting for."

Signed-off-by: Pierre-Louis Bossart pierre-louis.bossart@intel.com

core/pcm_lib.c | 8 ++++++-- core/pcm_native.c | 6 ++++++ include/asound.h | 4 ++++ include/pcm.h | 1 + pci/hda/hda_intel.c | 9 ++++++--- pci/oxygen/oxygen_pcm.c | 14 ++++++++++---- 6 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/core/pcm_lib.c b/core/pcm_lib.c index a1707cc..4963d8f 100644 --- a/core/pcm_lib.c +++ b/core/pcm_lib.c @@ -374,7 +374,8 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream, (unsigned long)runtime->hw_ptr_base); } /* something must be really wrong */

• if (delta >= runtime->buffer_size + runtime->period_size) {

• if (delta >= runtime->buffer_size + runtime->period_size &&

•        !runtime->no_period_irq) {
  

  hw_ptr_error(substream, "Unexpected hw_pointer value %s" "(stream=%i, pos=%ld, new_hw_ptr=%ld, "

@@ -395,6 +396,8 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream, */ if (runtime->hw.info & SNDRV_PCM_INFO_BATCH) goto no_jiffies_check;

•    if (runtime->no_period_irq)
  

•            goto no_jiffies_check;
  

  hdelta = delta; if (hdelta < runtime->delay) goto no_jiffies_check;

@@ -431,7 +434,8 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream, hw_base = new_hw_ptr - (new_hw_ptr % runtime->buffer_size); } no_jiffies_check:

• if (delta > runtime->period_size + runtime->period_size / 2) {

• if (delta > runtime->period_size + runtime->period_size / 2 &&

•        !runtime->no_period_irq) {
  

  hw_ptr_error(substream, "Lost interrupts? %s" "(stream=%i, delta=%ld, new_hw_ptr=%ld, "

Use one 'if' and a goto behind the last condition to simplify things.

diff --git a/core/pcm_native.c b/core/pcm_native.c index 8bc7cb3..92c8c59 100644 --- a/core/pcm_native.c +++ b/core/pcm_native.c @@ -412,6 +412,12 @@ static int snd_pcm_hw_params(struct snd_pcm_substream *substream, goto _error; }

•    if (params->info & SNDRV_PCM_INFO_NO_PERIOD_IRQ)
  

•            runtime->no_period_irq = !!(params->flags &
  

•                                        SNDRV_PCM_HW_PARAMS_NO_PERIOD_IRQ);
  

•    else
  

•            runtime->no_period_irq = 0;
  

• runtime->access = params_access(params); runtime->format = params_format(params); runtime->subformat = params_subformat(params);

diff --git a/include/asound.h b/include/asound.h index a1803ec..d4b5f2d 100644 --- a/include/asound.h +++ b/include/asound.h @@ -259,6 +259,7 @@ typedef int __bitwise snd_pcm_subformat_t; #define SNDRV_PCM_INFO_HALF_DUPLEX 0x00100000 /* only half duplex */ #define SNDRV_PCM_INFO_JOINT_DUPLEX 0x00200000 /* playback and capture stream are somewhat correlated */ #define SNDRV_PCM_INFO_SYNC_START 0x00400000 /* pcm support some kind of sync go */ +#define SNDRV_PCM_INFO_NO_PERIOD_IRQ 0x00800000 /* period interrupt can be disabled */ #define SNDRV_PCM_INFO_FIFO_IN_FRAMES 0x80000000 /* internal kernel flag - FIFO size is in frames */

typedef int __bitwise snd_pcm_state_t; @@ -334,6 +335,9 @@ typedef int snd_pcm_hw_param_t; #define SNDRV_PCM_HW_PARAM_LAST_INTERVAL SNDRV_PCM_HW_PARAM_TICK_TIME

#define SNDRV_PCM_HW_PARAMS_NORESAMPLE (1<<0) /* avoid rate resampling */ +#define SNDRV_PCM_HW_PARAMS_EXPORT_BUFFER (1<<1) /* export buffer */ +#define SNDRV_PCM_HW_PARAMS_NO_PERIOD_IRQ (1<<2) /* disable period

•                                                      interrupts */
  
  

struct snd_interval { unsigned int min, max;

The PCM protocol version should be increased.

diff --git a/include/pcm.h b/include/pcm.h index dfd9b76..9abb4aa 100644 --- a/include/pcm.h +++ b/include/pcm.h @@ -297,6 +297,7 @@ struct snd_pcm_runtime { unsigned int info; unsigned int rate_num; unsigned int rate_den;

•    bool no_period_irq;
  

I would use an unsigned int bit field rather than bool in this case to make addition in-line with other structures in this file.

Jaroslav

----- Jaroslav Kysela perex@perex.cz Linux Kernel Sound Maintainer ALSA Project, Red Hat, Inc.