[alsa-devel] [PATCH] ALSA - Replace msleep() with usleep_range() to save module loading time

[Takashi Iwai]

At Mon, 10 Dec 2012 14:20:32 +0800,
Wang Xingchao wrote:
> 
> msleep(1) is not so accurate and may cause almost 15ms delay in azx_reset().
> usleep_range() can reduce ~30ms loading time for Intel Haswell which has two HDA
> controllers.
> 
> Signed-off-by: Wang Xingchao <wangxingchao2011 at gmail.com>

Actually 1m is chosen as the smallest positive number for msleep, and
it doesn't mean that we need to wait for 1ms at least.  It could be
shorter than that if you care about the speed.

So, I'd  suggest to change the value to a smaller one, and change the
timeout check instead of counting the loop but a more objective way,
e.g. checking jiffies, in order to get further reduction.

For example, in the code below...


> ---
>  sound/pci/hda/hda_intel.c |    8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
> index eb48109..865df90 100644
> --- a/sound/pci/hda/hda_intel.c
> +++ b/sound/pci/hda/hda_intel.c
> @@ -1075,22 +1075,22 @@ static int azx_reset(struct azx *chip, int full_reset)
>  
>  	count = 50;
>  	while (azx_readb(chip, GCTL) && --count)
> -		msleep(1);
> +		usleep_range(1000, 1500);
>  
>  	/* delay for >= 100us for codec PLL to settle per spec
>  	 * Rev 0.9 section 5.5.1
>  	 */
> -	msleep(1);
> +	usleep_range(1000, 1500);

This can be reduced obviously, if we trust the comment.


thanks,

Takashi

>  
>  	/* Bring controller out of reset */
>  	azx_writeb(chip, GCTL, azx_readb(chip, GCTL) | ICH6_GCTL_RESET);
>  
>  	count = 50;
>  	while (!azx_readb(chip, GCTL) && --count)
> -		msleep(1);
> +		usleep_range(1000, 1500);
>  
>  	/* Brent Chartrand said to wait >= 540us for codecs to initialize */
> -	msleep(1);
> +	usleep_range(1000, 1500);
>  
>        __skip:
>  	/* check to see if controller is ready */
> -- 
> 1.7.9.5
>