Hi Andrew, Guenter,
On Fri, 31 Aug 2012 12:38:12 -0700, Andrew Morton wrote:
> On Fri, 31 Aug 2012 08:02:19 -0700
> Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
>
> > DIV_ROUND_CLOSEST returns a bad result for negative dividends:
> > DIV_ROUND_CLOSEST(-2, 2) = 0
> >
> > Most of the time this does not matter. However, in the hardware monitoring
> > subsystem, DIV_ROUND_CLOSEST is sometimes used on integers which can be
> > negative (such as temperatures).
> >
> > ...
> >
> > +
> > +/*
> > + * Divide positive or negative dividend by positive divisor and round
> > + * to closest integer. Result is undefined for negative divisors.
> > + */
> > #define DIV_ROUND_CLOSEST(x, divisor)( \
> > { \
> > - typeof(divisor) __divisor = divisor; \
> > - (((x) + ((__divisor) / 2)) / (__divisor)); \
> > + typeof(x) __x = x; \
> > + typeof(divisor) __d = divisor; \
> > + (((typeof(x))-1) >= 0 || (__x) >= 0) ? \
> > + (((__x) + ((__d) / 2)) / (__d)) : \
> > + (((__x) - ((__d) / 2)) / (__d)); \
> > } \
>
> Looks good to me.
My testing looks good too.
Acked-by: Jean Delvare <khali@xxxxxxxxxxxx>
> The patch causes no change in text size for
> kernel/sched/fair.o and drivers/cpuidle/governors/menu.o, so it seems
> that the cc trickery is working.
Indeed. I looked for test size increase, and for my config, besides
hwmon, I only spotted the following ones:
drivers/media/rc/mceusb.o
drivers/gpu/drm/i915/intel_pm.o
drivers/tty/serial/pch_uart.o
These don't look like hot paths, so I'd say we don't care. Plus the
intel_pm one can probably be solved by using an unsigned int, I don't
see why/how ia_freq could be negative (negative frequency anyone?) And
for mceusb it can be solved easily by changing "1" to "1U".
For hwmon drivers, we typically only use DIV_ROUND_CLOSEST when the
user changes a setting, this isn't a frequent event. Plus, this is
exactly the case we are fixing here, as temperature limits, and to a
lesser extent voltage limits, can be negative.
> I'll add it to my tree for testing - please merge this via your tree.
--
Jean Delvare
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