linux-kernel - Re: [PATCH RFC] staging: wilc1000: give usleep

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Date:   Tue, 9 Apr 2019 03:36:56 +0200
From:   Nicholas Mc Guire <der.herr@...r.at>
To:     Adham.Abozaeid@...rochip.com
Cc:     hofrat@...dl.org, Ajay.Kathat@...rochip.com,
        gregkh@...uxfoundation.org, linux-wireless@...r.kernel.org,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] staging: wilc1000: give usleep_range a range

On Mon, Apr 08, 2019 at 09:10:00PM +0000, Adham.Abozaeid@...rochip.com wrote:
> Hi Nicholas
> 
> On 4/6/19 5:01 AM, Nicholas Mc Guire wrote:
> > External E-Mail
> >
> >
> > Someone that knows the motivation for setting the time to 2 millisecond
> > might need to check if the 2 milliseconds where seen as tollerable max or
> > min - I'm assuming it was the min so extending.
> 
> 2 msec is the time the chip takes to wake up from sleep.
> 
> Increasing the maximum to 5 msec will impact the throughput since this call is on the transmit path.
> 

ok - would it be tollerable to make it 2 - 2.5 ms ?
even that would allow for the hrtimer subsystem to optimize
a lot. In any case the min==max case gives you very little
if you run a test-case with usleep_range(1000,1000) and
a loop with usleep_range(1000,2000) and look at the distribution
you will have a hard time seeing any difference.

I doubt you would readily see the change from usleep_range(2000,2000)
to usleep_range(2000,3000) in benchmarks - maybe (2000,5000) would
be visible.

My assumption (I have not analyzed it in detail) is that if
you have a high re-use of existing timers that the setup of the timer
is faster and thats why increasing the range > 0 can actually result
in better jitter distribution.

thx!
hofrat

> > diff --git a/drivers/staging/wilc1000/wilc_wlan.c b/drivers/staging/wilc1000/wilc_wlan.c
> > index c238969..42da533 100644
> > --- a/drivers/staging/wilc1000/wilc_wlan.c
> > +++ b/drivers/staging/wilc1000/wilc_wlan.c
> > @@ -408,7 +408,7 @@ void chip_wakeup(struct wilc *wilc)
> >  			wilc->hif_func->hif_write_reg(wilc, 1, reg & ~BIT(1));
> >  
> >  			do {
> > -				usleep_range(2 * 1000, 2 * 1000);
> > +				usleep_range(2 * 1000, 5 * 1000);
> >  				wilc_get_chipid(wilc, true);
> >  			} while (wilc_get_chipid(wilc, true) == 0);
> >  		} while (wilc_get_chipid(wilc, true) == 0);
> > @@ -423,7 +423,7 @@ void chip_wakeup(struct wilc *wilc)
> >  						     &clk_status_reg);
> >  
> >  			while ((clk_status_reg & 0x1) == 0) {
> > -				usleep_range(2 * 1000, 2 * 1000);
> > +				usleep_range(2 * 1000, 5 * 1000);
> >  
> >  				wilc->hif_func->hif_read_reg(wilc, 0xf1,
> >  							     &clk_status_reg);
> 
> 
> Thanks,
> 
> Adham
>