On Mon, 28 Sep 2015 23:28:34 +0200 Andrea Arcangeli <aarca...@redhat.com> wrote:
> During boot I get a div by zero Oops regression starting in v4.3-rc3. > > ... > > --- a/drivers/thermal/power_allocator.c > +++ b/drivers/thermal/power_allocator.c > @@ -144,6 +144,16 @@ static void estimate_pid_constants(struct > thermal_zone_device *tz, > switch_on_temp = 0; > > temperature_threshold = control_temp - switch_on_temp; > + /* > + * estimate_pid_constants() tries to find appropriate default > + * values for thermal zones that don't provide them. If a > + * system integrator has configured a thermal zone with two > + * passive trip points at the same temperature, that person > + * hasn't put any effort to set up the thermal zone properly > + * so just give up. > + */ > + if (!temperature_threshold) > + return; > > if (!tz->tzp->k_po || force) > tz->tzp->k_po = int_to_frac(sustainable_power) / a) Are we sure this won't leave tz->tzp fields uninitialized? b) I'm not understanding that code at all. The "proportional" term in a PID controller is supposed to be proportional to the (desired - actual) difference (aka "the error"). But estimate_pid_constants() appears to be setting the "proportional" term to be proportional to 1/error! Maybe a description of local `temperature_threshold' would help clue me in. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
