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Message-ID: <175179607401.406.16648050119866359640.tip-bot2@tip-bot2>
Date: Sun, 06 Jul 2025 10:01:14 -0000
From: "tip-bot2 for Rik van Riel" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Jann Horn <jannh@...gle.com>, Rik van Riel <riel@...riel.com>,
Thomas Gleixner <tglx@...utronix.de>,
"Yury Norov (NVIDIA)" <yury.norov@...il.com>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [tip: smp/core] smp: Wait only if work was enqueued
The following commit has been merged into the smp/core branch of tip:
Commit-ID: 946a7281982530d333eaee62bd1726f25908b3a9
Gitweb: https://git.kernel.org/tip/946a7281982530d333eaee62bd1726f25908b3a9
Author: Rik van Riel <riel@...riel.com>
AuthorDate: Wed, 02 Jul 2025 13:52:54 -04:00
Committer: Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Sun, 06 Jul 2025 11:57:39 +02:00
smp: Wait only if work was enqueued
Whenever work is enqueued for a remote CPU, smp_call_function_many_cond()
may need to wait for that work to be completed. However, if no work is
enqueued for a remote CPU, because the condition func() evaluated to false
for all CPUs, there is no need to wait.
Set run_remote only if work was enqueued on remote CPUs.
Document the difference between "work enqueued", and "CPU needs to be
woken up"
Suggested-by: Jann Horn <jannh@...gle.com>
Signed-off-by: Rik van Riel <riel@...riel.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Yury Norov (NVIDIA) <yury.norov@...il.com>
Link: https://lore.kernel.org/all/20250703203019.11331ac3@fangorn
---
kernel/smp.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/kernel/smp.c b/kernel/smp.c
index 99d1fd0..c5e1da7 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -802,7 +802,6 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
/* Check if we need remote execution, i.e., any CPU excluding this one. */
if (cpumask_any_and_but(mask, cpu_online_mask, this_cpu) < nr_cpu_ids) {
- run_remote = true;
cfd = this_cpu_ptr(&cfd_data);
cpumask_and(cfd->cpumask, mask, cpu_online_mask);
__cpumask_clear_cpu(this_cpu, cfd->cpumask);
@@ -816,6 +815,9 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
continue;
}
+ /* Work is enqueued on a remote CPU. */
+ run_remote = true;
+
csd_lock(csd);
if (wait)
csd->node.u_flags |= CSD_TYPE_SYNC;
@@ -827,6 +829,10 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
#endif
trace_csd_queue_cpu(cpu, _RET_IP_, func, csd);
+ /*
+ * Kick the remote CPU if this is the first work
+ * item enqueued.
+ */
if (llist_add(&csd->node.llist, &per_cpu(call_single_queue, cpu))) {
__cpumask_set_cpu(cpu, cfd->cpumask_ipi);
nr_cpus++;
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