On 26 March 2015 at 18:38, Morten Rasmussen <[email protected]> wrote: > On Wed, Mar 25, 2015 at 06:08:42PM +0000, Vincent Guittot wrote: >> On 25 March 2015 at 18:33, Peter Zijlstra <[email protected]> wrote: >> > On Tue, Mar 24, 2015 at 11:00:57AM +0100, Vincent Guittot wrote: >> >> On 23 March 2015 at 14:19, Peter Zijlstra <[email protected]> wrote: >> >> > On Fri, Feb 27, 2015 at 04:54:07PM +0100, Vincent Guittot wrote: >> >> > >> >> >> + unsigned long scale_freq = arch_scale_freq_capacity(NULL, cpu); >> >> > >> >> >> + sa->running_avg_sum += delta_w * scale_freq >> >> >> + >> SCHED_CAPACITY_SHIFT; >> >> > >> >> > so the only thing that could be improved is somehow making this >> >> > multiplication go away when the arch doesn't implement the function. >> >> > >> >> > But I'm not sure how to do that without #ifdef. >> >> > >> >> > Maybe a little something like so then... that should make the compiler >> >> > get rid of those multiplications unless the arch needs them. >> >> >> >> yes, it removes useless multiplication when not used by an arch. >> >> It also adds a constraint on the arch side which have to define >> >> arch_scale_freq_capacity like below: >> >> >> >> #define arch_scale_freq_capacity xxx_arch_scale_freq_capacity >> >> with xxx_arch_scale_freq_capacity an architecture specific function >> > >> > Yeah, but it not being weak should make that a compile time warn/fail, >> > which should be pretty easy to deal with. >> > >> >> If it sounds acceptable i can update the patch with your proposal ? >> > >> > I'll stick it to the end, I just wanted to float to patch to see if >> > people had better solutions. >> >> ok. all other methods that i have tried, was removing the optimization >> when default arch_scale_freq_capacity was used > > Another potential solution is to stay with weak functions but move the > multiplication and shift into the arch_scale_*() functions by passing > the value we want to scale into the arch_scale_*() function. That way we > can completely avoid multiplication and shift in the default case (no > arch_scale*() implementations, which is better than what we have today.
the sched_rt_avg_update only uses the mul with arch_scale_freq_capacity because the shift by SCHED_CAPACITY_SHIFT has been factorized in scale_rt_capacity > > The only downside is that for frequency invariance we need three > arch_scale_freq_capacity() calls instead of two. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
