On Tue, Mar 24, 2015 at 11:00:57AM +0100, Vincent Guittot wrote:
On 23 March 2015 at 14:19, Peter Zijlstra peterz@infradead.org 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.