On 09/02/2022, Bjorn Helgaas wrote: > On Wed, Aug 17, 2022 at 11:08:21PM +0000, Will McVicker wrote: > > From: Sajid Dalvi <sdalvi@xxxxxxxxxx> > > > > Since the PCI spec requires a 10ms D3Hot delay (defined by > > PCI_PM_D3HOT_WAIT) and a few of the PCI quirks update the D3Hot delay up > > to 120ms, let's add support for both usleep_range and msleep based on > > the delay time to improve the delay accuracy. > > > > This patch is based off of a commit from Sajid Dalvi <sdalvi@xxxxxxxxxx> > > in the Pixel 6 kernel tree [1]. Testing on a Pixel 6, found that the > > 10ms delay for the Exynos PCIe device was on average delaying for 19ms > > when the spec requires 10ms. Switching from msleep to uslseep_range > > therefore decreases the resume time on a Pixel 6 on average by 9ms. > > Add the "PCIe r6.0, sec 5.9" spec reference for the 10ms delay for > transitions to or from D3hot. > > s/D3Hot/D3hot/ to match other usage (at least in Linux; the spec does > use "D3Hot") > > s/uslseep_range/usleep_range/ > > Add "()" after function names. Thanks for the suggestions! I'll update these in the next patchset. > > In the subject, "Switch ... to *also* use usleep_range": what does the > "also" mean? It sounds like it's referring to some other place where > we also use usleep_range()? I was intending to mean usleep_range() will be used when the the delay <=20 ms, else msleep() will be used. If we drop msleep() altogether as suggested in your comments below, then I can change this to be: "Switch D3hot delay to use usleep_range." > > > [1] https://android.googlesource.com/kernel/gs/+/18a8cad68d8e6d50f339a716a18295e6d987cee3 > > > > Signed-off-by: Sajid Dalvi <sdalvi@xxxxxxxxxx> > > Signed-off-by: Will McVicker <willmcvicker@xxxxxxxxxx> > > --- > > drivers/pci/pci.c | 16 +++++++++++----- > > 1 file changed, 11 insertions(+), 5 deletions(-) > > > > v3: > > * Use DIV_ROUND_CLOSEST instead of bit manipulation. > > * Minor refactor to use max() where relavant. > > > > v2: > > * Update to use 20-25% upper bound > > * Update to use usleep_range() for <=20ms, else use msleep() > > > > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c > > index 95bc329e74c0..cfa8386314f2 100644 > > --- a/drivers/pci/pci.c > > +++ b/drivers/pci/pci.c > > @@ -66,13 +66,19 @@ struct pci_pme_device { > > > > static void pci_dev_d3_sleep(struct pci_dev *dev) > > { > > - unsigned int delay = dev->d3hot_delay; > > + unsigned int delay_ms = max(dev->d3hot_delay, pci_pm_d3hot_delay); > > > > - if (delay < pci_pm_d3hot_delay) > > - delay = pci_pm_d3hot_delay; > > + if (delay_ms) { > > + if (delay_ms <= 20) { > > + /* Use a 20% upper bound with 1ms minimum */ > > + unsigned int upper = max(DIV_ROUND_CLOSEST(delay_ms, 5), 1U); > > > > - if (delay) > > - msleep(delay); > > + usleep_range(delay_ms * USEC_PER_MSEC, > > + (delay_ms + upper) * USEC_PER_MSEC); > > + } else { > > + msleep(delay_ms); > > I hate the fact that we have to check for those ancient Intel chips at > all, but having to read through the usleep_range() vs msleep() thing > is just painful. > > fsleep() would be much simpler, but I am sympathetic that the fsleep() > range of 10-20ms probably wouldn't get the benefit you want. > > I wish Documentation/timers/timers-howto.rst included a reason why we > should use msleep() instead of usleep_range() for longer sleeps. Is > there a reason not to do this: I'm not familiar with the reasons behind these two beside what the documentation states. I don't know what happens when you use usleep_range() with a delay >20ms. > > static void pci_dev_d3_sleep(struct pci_dev *dev) > { > unsigned int delay_ms = max(dev->d3hot_delay, pci_pm_d3hot_delay); > unsigned int upper; > > if (delay_ms) { > /* 20% upper bound, 1ms minimum */ > upper = max(DIV_ROUND_CLOSEST(delay_ms, 5), 1U) > usleep_range(delay_ms * USEC_PER_MSEC, > (delay_ms + upper) * USEC_PER_MSEC); > } > } > > Since the Intel quirk is for 120ms, a 20% upper bound would make the > range 120-144ms. Would that be a problem? Those chips are ancient; > the list is untouched since it was added in 2006. The point of > usleep_range() is to allow the scheduler to coalesce the wakeup with > other events, so it seems unlikely we'd ever wait the whole 144ms. I > vote for optimizing the readability over sleep/resume time for > already-broken chips. I'm totally fine with this, but I don't really know what the impact would be to those old Intel chips. > > Bjorn Thanks, Will
