| Message ID | 20831b8d237bf3a20e4e328286f678b425ff04c9.1524738578.git.viresh.kumar@linaro.org |
|---|---|
| State | Accepted |
| Commit | f1d88b4468188ddcd2620b8d612068faf6662a62 |
| Headers | show |
| Series | [V2,1/2] sched/fair: Rearrange select_task_rq_fair() to optimize it | expand |
Hi, LGTM. Tiny inline comment but TBH might not be worth it. FWIW: Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> On 26/04/18 11:30, Viresh Kumar wrote: > Rearrange select_task_rq_fair() a bit to avoid executing some > conditional statements in few specific code-paths. That gets rid of the > goto as well. > > This shouldn't result in any functional changes. > > Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> > Tested-by: Rohit Jain <rohit.k.jain@oracle.com> > > --- > V1->V2: > - Optimize a bit more and get rid of affine_sd variable (Valentin) > - Add unlikely while checking for non-NULL sd and add fast/slow path > comments (Joel) > - Add tested-by from Rohit. > > kernel/sched/fair.c | 37 ++++++++++++++++--------------------- > 1 file changed, 16 insertions(+), 21 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 54dc31e7ab9b..84fc74ddbd4b 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6613,7 +6613,7 @@ static int wake_cap(struct task_struct *p, int cpu, int prev_cpu) > static int > select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_flags) > { > - struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL; > + struct sched_domain *tmp, *sd = NULL; > int cpu = smp_processor_id(); > int new_cpu = prev_cpu; > int want_affine = 0; > @@ -6636,7 +6636,10 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f > */ > if (want_affine && (tmp->flags & SD_WAKE_AFFINE) && > cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) { > - affine_sd = tmp; > + if (cpu != prev_cpu) > + new_cpu = wake_affine(tmp, p, cpu, prev_cpu, sync); This cpu != prev_cpu check could be folded into wake_affine() to make this look a little neater, but we might want to keep things as is to avoid a function call (it's only ever called once so it might get inlined, but AFAIK that's not guaranteed). > + > + sd = NULL; /* Prefer wake_affine over balance flags */ > break; > } > > @@ -6646,33 +6649,25 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f > break; > } > > - if (affine_sd) { > - sd = NULL; /* Prefer wake_affine over balance flags */ > - if (cpu == prev_cpu) > - goto pick_cpu; > - > - new_cpu = wake_affine(affine_sd, p, cpu, prev_cpu, sync); > - } > + if (unlikely(sd)) { > + /* Slow path */ > > - if (sd && !(sd_flag & SD_BALANCE_FORK)) { > /* > * We're going to need the task's util for capacity_spare_wake > * in find_idlest_group. Sync it up to prev_cpu's > * last_update_time. > */ > - sync_entity_load_avg(&p->se); > - } > - > - if (!sd) { > -pick_cpu: > - if (sd_flag & SD_BALANCE_WAKE) { /* XXX always ? */ > - new_cpu = select_idle_sibling(p, prev_cpu, new_cpu); > + if (!(sd_flag & SD_BALANCE_FORK)) > + sync_entity_load_avg(&p->se); > > - if (want_affine) > - current->recent_used_cpu = cpu; > - } > - } else { > new_cpu = find_idlest_cpu(sd, p, cpu, prev_cpu, sd_flag); > + } else if (sd_flag & SD_BALANCE_WAKE) { /* XXX always ? */ > + /* Fast path */ > + > + new_cpu = select_idle_sibling(p, prev_cpu, new_cpu); > + > + if (want_affine) > + current->recent_used_cpu = cpu; > } > rcu_read_unlock(); > >
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 54dc31e7ab9b..84fc74ddbd4b 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6613,7 +6613,7 @@ static int wake_cap(struct task_struct *p, int cpu, int prev_cpu) static int select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_flags) { - struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL; + struct sched_domain *tmp, *sd = NULL; int cpu = smp_processor_id(); int new_cpu = prev_cpu; int want_affine = 0; @@ -6636,7 +6636,10 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f */ if (want_affine && (tmp->flags & SD_WAKE_AFFINE) && cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) { - affine_sd = tmp; + if (cpu != prev_cpu) + new_cpu = wake_affine(tmp, p, cpu, prev_cpu, sync); + + sd = NULL; /* Prefer wake_affine over balance flags */ break; } @@ -6646,33 +6649,25 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f break; } - if (affine_sd) { - sd = NULL; /* Prefer wake_affine over balance flags */ - if (cpu == prev_cpu) - goto pick_cpu; - - new_cpu = wake_affine(affine_sd, p, cpu, prev_cpu, sync); - } + if (unlikely(sd)) { + /* Slow path */ - if (sd && !(sd_flag & SD_BALANCE_FORK)) { /* * We're going to need the task's util for capacity_spare_wake * in find_idlest_group. Sync it up to prev_cpu's * last_update_time. */ - sync_entity_load_avg(&p->se); - } - - if (!sd) { -pick_cpu: - if (sd_flag & SD_BALANCE_WAKE) { /* XXX always ? */ - new_cpu = select_idle_sibling(p, prev_cpu, new_cpu); + if (!(sd_flag & SD_BALANCE_FORK)) + sync_entity_load_avg(&p->se); - if (want_affine) - current->recent_used_cpu = cpu; - } - } else { new_cpu = find_idlest_cpu(sd, p, cpu, prev_cpu, sd_flag); + } else if (sd_flag & SD_BALANCE_WAKE) { /* XXX always ? */ + /* Fast path */ + + new_cpu = select_idle_sibling(p, prev_cpu, new_cpu); + + if (want_affine) + current->recent_used_cpu = cpu; } rcu_read_unlock();