Hi Rohit,
On Mon, Sep 25, 2017 at 9:40 PM, Rohit Jain rohit.k.jain@oracle.com wrote:
On 09/25/2017 07:51 PM, joelaf wrote:
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On 09/25/2017 05:02 PM, Rohit Jain wrote:
While looking for idle CPUs for a waking task, we should also account for the delays caused due to the bandwidth reduction by RT/IRQ tasks.
This patch does that by trying to find a higher capacity CPU with minimum wake up latency.
Signed-off-by: Rohit Jain rohit.k.jain@oracle.com
kernel/sched/fair.c | 27 ++++++++++++++++++++++++--- 1 file changed, 24 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index eca6a57..afb701f 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5590,6 +5590,11 @@ static unsigned long capacity_orig_of(int cpu) return cpu_rq(cpu)->cpu_capacity_orig; } +static inline bool full_capacity(int cpu) +{
return (capacity_of(cpu) >= (capacity_orig_of(cpu)*819 >> 10));Wouldn't 768 be better for multiplication? gcc converts the expression to shifts and adds then.
While 768 is easier to convert to shifts and adds, 819/1024 gets you very close to 80% which is what I was trying to achieve.
Yeah I guess if its not too hard, you could check if 768 gets you a similar result but I would defer to the maintainers on what they are Ok with.
+}
- static unsigned long cpu_avg_load_per_task(int cpu) { struct rq *rq = cpu_rq(cpu);
@@ -5916,8 +5921,10 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu) unsigned long load, min_load = ULONG_MAX; unsigned int min_exit_latency = UINT_MAX; u64 latest_idle_timestamp = 0;
unsigned int backup_cap = 0; int least_loaded_cpu = this_cpu; int shallowest_idle_cpu = -1;int shallowest_idle_cpu_backup = -1; int i; /* Check if we have any choice: */@@ -5937,7 +5944,12 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu) */ min_exit_latency = idle->exit_latency; latest_idle_timestamp = rq->idle_stamp;
shallowest_idle_cpu = i;
if (full_capacity(i)) {shallowest_idle_cpu = i;} else if (capacity_of(i) > backup_cap) {shallowest_idle_cpu_backup = i;backup_cap = capacity_of(i);}I'm a bit skeptical about this - if the CPU is idle, then is it likely that the capacity of the CPU is reduced due to RT pressure?
What has idleness got to do with RT pressure?
This is an instantaneous view where the scheduler is looking to place threads. In this case, if we know historically the capacity of the CPU is reduced (due to RT/IRQ/Thermal Throttling or whatever it may be) we should avoid that CPU if we have a choice.
Yeah Ok, that's a fair point, I don't dispute this fact. I was just trying to understand your patch.
thanks,
- Joel
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