`On Mon, Mar 07, 2022 at 01:04:50PM -0800, Bjorn Andersson wrote:> On Mon 07 Mar 08:13 PST 2022, Andy Shevchenko wrote:> > On Mon, Mar 07, 2022 at 06:48:25AM -0800, Bjorn Andersson wrote:> > > On Mon 07 Mar 02:16 PST 2022, Andy Shevchenko wrote:> > > > On Sun, Mar 06, 2022 at 07:40:40PM -0800, Bjorn Andersson wrote:...> > > > > +		/* 15us to allow the SBU switch to turn off */> > > > > +		usleep_range(15, 1000);> > > > > > > > This is quite unusual range.> > > > > > > > If you are fine with the long delay, why to stress the system on it?> > > > Otherwise the use of 1000 is unclear.> > > > > > > > That said, I would expect one of the below:> > > > > > > > 		usleep_range(15, 30);> > > > 		usleep_range(500, 1000);> > > > > > Glad you asked about that, as you say the typical form is to keep the> > > range within 2x of the lower value, or perhaps lower + 5.> > > > > > But if the purpose is to specify a minimum time and then give a max to> > > give the system some flexibility in it's decision of when to wake up.> > > And in situations such as this, we're talking about someone connecting a> > > cable, so we're in "no rush" and I picked the completely arbitrary 1ms> > > as the max.> > > > > > Do you see any drawback of this much higher number? (Other than it> > > looking "wrong")> > > > I see the drawback of low number.> > 15us is based on the data sheet and if the kernel is ready to serve us> after 15us then let's do that.> > > The 1000 makes not much sense to me with the minimum 66x times less.> > If there is no rush, use some reasonable values,> > what about> > > > 		usleep_range(100, 1000);> > > > ? 10x is way better than 66x.> > I don't agree, and in particular putting 100 here because it's 1/10 of> the number I just made up doesn't sounds like a good reason. The> datasheet says 15us, so that is at least based on something real.> > In https://www.kernel.org/doc/Documentation/timers/timers-howto.txt> I find the following:> >     With the introduction of a range, the scheduler is>     free to coalesce your wakeup with any other wakeup>     that may have happened for other reasons, or at the>     worst case, fire an interrupt for your upper bound.> >     The larger a range you supply, the greater a chance>     that you will not trigger an interrupt; this should>     be balanced with what is an acceptable upper bound on>     delay / performance for your specific code path. Exact>     tolerances here are very situation specific, thus it>     is left to the caller to determine a reasonable range.> > Which to me says that the wider range is perfectly reasonable. In> particular 15, 30 (which seems to be quite common) makes the available> range to the scheduler unnecessarily narrow.> > And it's clear that whatever the upper bound it's going to be some> arbitrary number, but 1ms should ensure that there are other hrtimer> interrupts to piggy back on.Okay, I have grepped for usleep_range(x[x], yyyy) and there are 9 modulesuse it. A few commit messages call 1000 as "reasonable upper limit".-- With Best Regards,Andy Shevchenko`