On Tue, Nov 25, 2014 at 01:48:02PM +0000, Vincent Guittot wrote:
On 24 November 2014 at 18:05, Morten Rasmussen morten.rasmussen@arm.com wrote:
On Mon, Nov 24, 2014 at 02:24:00PM +0000, Vincent Guittot wrote:
On 21 November 2014 at 13:35, Morten Rasmussen morten.rasmussen@arm.com wrote:
On Mon, Nov 03, 2014 at 04:54:42PM +0000, Vincent Guittot wrote:
[snip]
The average running time of RT tasks is used to estimate the remaining compute @@ -5801,19 +5801,12 @@ static unsigned long scale_rt_capacity(int cpu)
total = sched_avg_period() + delta;
if (unlikely(total < avg)) {/* Ensures that capacity won't end up being negative */available = 0;} else {available = total - avg;}
used = div_u64(avg, total);I haven't looked through all the details of the rt avg tracking, but if 'used' is in the range [0..SCHED_CAPACITY_SCALE], I believe it should work. Is it guaranteed that total > 0 so we don't get division by zero?
static inline u64 sched_avg_period(void) { return (u64)sysctl_sched_time_avg * NSEC_PER_MSEC / 2; }
I see.
It does get a slightly more complicated if we want to figure out the available capacity at the current frequency (current < max) later. Say, rt eats 25% of the compute capacity, but the current frequency is only 50%. In that case get:
curr_avail_capacity = (arch_scale_cpu_capacity() * (arch_scale_freq_capacity() - (SCHED_SCALE_CAPACITY - scale_rt_capacity())))
SCHED_CAPACITY_SHIFT
You don't have to be so complicated but simply need to do: curr_avail_capacity for CFS = (capacity_of(CPU) * arch_scale_freq_capacity()) >> SCHED_CAPACITY_SHIFT
capacity_of(CPU) = 600 is the max available capacity for CFS tasks once we have removed the 25% of capacity that is used by RT tasks arch_scale_freq_capacity = 512 because we currently run at 50% of max freq
so curr_avail_capacity for CFS = 300
I don't think that is correct. It is at least not what I had in mind.
capacity_orig_of(cpu) = 800, we run at 50% frequency which means:
curr_capacity = capacity_orig_of(cpu) * arch_scale_freq_capacity() >> SCHED_CAPACITY_SHIFT = 400
So the total capacity at the current frequency (50%) is 400, without considering RT. scale_rt_capacity() is frequency invariant, so it takes away capacity_orig_of(cpu) - capacity_of(cpu) = 200 worth of capacity for RT. We need to subtract that from the current capacity to get the available capacity at the current frequency.
curr_available_capacity = curr_capacity - (capacity_orig_of(cpu) - capacity_of(cpu)) = 200
you're right, this one looks good to me too
Okay, thanks for confirming. It doesn't affect this patch set anyway, I just wanted to be sure that I got all the scaling factors right :)