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sched/balancing: Switch the 'DEFINE_SPINLOCK(balancing)' spinlock into an 'atomic_t sched_balance_running' flag
The 'balancing' spinlock added in:
08c183f31b
("[PATCH] sched: add option to serialize load balancing")
... is taken when the SD_SERIALIZE flag is set in a domain, but in reality it
is a glorified global atomic flag serializing the load-balancing of
those domains.
It doesn't have any explicit locking semantics per se: we just
spin_trylock() it.
Turn it into a ... global atomic flag. This makes it more
clear what is going on here, and reduces overhead and code
size a bit:
# kernel/sched/fair.o: [x86-64 defconfig]
text data bss dec hex filename
60730 2721 104 63555 f843 fair.o.before
60718 2721 104 63543 f837 fair.o.after
Also document the flag a bit.
No change in functionality intended.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://lore.kernel.org/r/20240308105901.1096078-2-mingo@kernel.org
This commit is contained in:
parent
855684c7d9
commit
214c1b7f13
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@ -11633,7 +11633,20 @@ static int active_load_balance_cpu_stop(void *data)
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return 0;
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}
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static DEFINE_SPINLOCK(balancing);
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/*
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* This flag serializes load-balancing passes over large domains
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* (above the NODE topology level) - only one load-balancing instance
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* may run at a time, to reduce overhead on very large systems with
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* lots of CPUs and large NUMA distances.
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*
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* - Note that load-balancing passes triggered while another one
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* is executing are skipped and not re-tried.
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*
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* - Also note that this does not serialize rebalance_domains()
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* execution, as non-SD_SERIALIZE domains will still be
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* load-balanced in parallel.
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*/
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static atomic_t sched_balance_running = ATOMIC_INIT(0);
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/*
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* Scale the max load_balance interval with the number of CPUs in the system.
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@ -11711,7 +11724,7 @@ static void rebalance_domains(struct rq *rq, enum cpu_idle_type idle)
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need_serialize = sd->flags & SD_SERIALIZE;
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if (need_serialize) {
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if (!spin_trylock(&balancing))
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if (atomic_cmpxchg_acquire(&sched_balance_running, 0, 1))
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goto out;
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}
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@ -11729,7 +11742,7 @@ static void rebalance_domains(struct rq *rq, enum cpu_idle_type idle)
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interval = get_sd_balance_interval(sd, busy);
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}
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if (need_serialize)
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spin_unlock(&balancing);
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atomic_set_release(&sched_balance_running, 0);
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out:
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if (time_after(next_balance, sd->last_balance + interval)) {
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next_balance = sd->last_balance + interval;
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