On 07/10/2015 01:19 AM, Mike Galbraith wrote:
On Thu, 2015-07-09 at 15:26 +0200, Peter Zijlstra wrote:
On Wed, Jul 08, 2015 at 08:13:46AM +0200, Mike Galbraith wrote:
static int wake_wide(struct task_struct *p)
{
+ unsigned int waker_flips = current->wakee_flips;
+ unsigned int wakee_flips = p->wakee_flips;
int factor = this_cpu_read(sd_llc_size);
+ if (waker_flips < wakee_flips)
+ swap(waker_flips, wakee_flips);
This makes the wakee/waker names useless, the end result is more like
wakee_flips := client_flips, waker_flips := server_flips.
I settled on master/slave plus hopefully improved comment block.
+ if (wakee_flips < factor || waker_flips < wakee_flips * factor)
+ return 0;
I don't get the first condition... why would the client ever flip? It
only talks to that one server.
(tightening heuristic up a bit by one means or another would be good,
but "if it ain't broke, don't fix it" applies for this patchlet)
@@ -5021,14 +5015,17 @@ select_task_rq_fair(struct task_struct *
{
struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL;
int cpu = smp_processor_id();
+ int new_cpu = prev_cpu;
int want_affine = 0;
int sync = wake_flags & WF_SYNC;
rcu_read_lock();
+ if (sd_flag & SD_BALANCE_WAKE) {
+ want_affine = !wake_wide(p) && cpumask_test_cpu(cpu,
tsk_cpus_allowed(p));
+ if (!want_affine)
+ goto select_idle;
+ }
So this preserves/makes worse the bug Morten spotted, even without
want_affine we should still attempt SD_BALANCE_WAKE if set.
Fixed. wake_wide() may override want_affine as before, want_affine may
override other ->flags as before, but a surviving domain selection now
results in a full balance instead of a select_idle_sibling() call.
sched: beef up wake_wide()
Josef Bacik reported that Facebook sees better performance with their
1:N load (1 dispatch/node, N workers/node) when carrying an old patch
to try very hard to wake to an idle CPU. While looking at wake_wide(),
I noticed that it doesn't pay attention to the wakeup of a many partner
waker, returning 1 only when waking one of its many partners.
Correct that, letting explicit domain flags override the heuristic.
While at it, adjust task_struct bits, we don't need a 64bit counter.
Signed-off-by: Mike Galbraith <umgwanakikb...@gmail.com>
Tested-by: Josef Bacik <jba...@fb.com>
Not quite as awesome but still better than the baseline so we're good.
Thanks,
Josef
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