Quoting Mika Kuoppala (2018-04-20 10:54:26) > We use jiffies to determine when wait expires. However > Imre did find out that jiffies can and will do a >1 > increments on certain situations [1]. When this happens > in a wait_for loop, we return timeout errorneously > much earlier than what the real wallclock would say. > > We can't afford our waits to timeout prematurely. > Discard jiffies and change to ktime to detect timeouts. > > Reported-by: Imre Deak <imre.deak@xxxxxxxxx> > References: https://lkml.org/lkml/2018/4/18/798 [1] > Cc: Imre Deak <imre.deak@xxxxxxxxx> > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > Signed-off-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx> The atomic variant is already jiffie-less (since it has to work in irq-off contexts). Maybe a bit tricky to suggest that the callers know if jiffie incremens are accurate or not. What is not clear from the link is whether our wait_for() is running across suspend, or whether it is just jiffie recalibration some time during resume that breaks. > drivers/gpu/drm/i915/intel_drv.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h > index 8b20824e806e..ac7565220aa3 100644 > --- a/drivers/gpu/drm/i915/intel_drv.h > +++ b/drivers/gpu/drm/i915/intel_drv.h > @@ -49,12 +49,12 @@ > * check the condition before the timeout. > */ > #define __wait_for(OP, COND, US, Wmin, Wmax) ({ \ > - unsigned long timeout__ = jiffies + usecs_to_jiffies(US) + 1; \ > + const ktime_t end__ = ktime_add_ns(ktime_get_raw(), 1000ll * (US)); \ > long wait__ = (Wmin); /* recommended min for usleep is 10 us */ \ > int ret__; \ > might_sleep(); \ > for (;;) { \ > - bool expired__ = time_after(jiffies, timeout__); \ > + const bool expired__ = ktime_after(ktime_get_raw(), end__); \ > OP; \ > if (COND) { \ > ret__ = 0; \ Nevertheless, the patch is ok and I don't have too much objection to adding another tsc (at best, hpet at worst!) read around every mmio+sleep, plus expanding the code for the function calls. Out of curiosity what is the size delta? How many wait_for() do we have left that we need to convert to a function call rather than macro expansion? Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Cc stable? -Chris _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
