linux-kernel - [PATCH 1/2] membarrier: allow cpu

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Message-ID: <20250626155257.81256-2-dyudaken@gmail.com>
Date: Thu, 26 Jun 2025 16:52:56 +0100
From: Dylan Yudaken <dyudaken@...il.com>
To: mathieu.desnoyers@...icios.com,
	paulmck@...nel.org
Cc: mingo@...hat.com,
	peterz@...radead.org,
	juri.lelli@...hat.com,
	vincent.guittot@...aro.org,
	dietmar.eggemann@....com,
	rostedt@...dmis.org,
	bsegall@...gle.com,
	mgorman@...e.de,
	vschneid@...hat.com,
	shuah@...nel.org,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	Dylan Yudaken <dyudaken@...il.com>
Subject: [PATCH 1/2] membarrier: allow cpu_id to be set on more commands

No reason to not allow MEMBARRIER_CMD_FLAG_CPU on
MEMBARRIER_CMD_PRIVATE_EXPEDITED or
MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE.

If it is known specifically what cpu you want to interrupt then there
is a decent efficiency saving in not interrupting all the other ones.

Also - the code already works as is for them.

Signed-off-by: Dylan Yudaken <dyudaken@...il.com>
---
 kernel/sched/membarrier.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
index 809194cd779f..def6d4094ad6 100644
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c
@@ -595,7 +595,9 @@ static int membarrier_get_registrations(void)
  *          contains the CPU on which to interrupt (= restart)
  *          the RSEQ critical section.
  * @cpu_id: if @flags == MEMBARRIER_CMD_FLAG_CPU, indicates the cpu on which
- *          RSEQ CS should be interrupted (@cmd must be
+ *          RSEQ CS should be interrupted (@cmd must be one of
+ *          MEMBARRIER_CMD_PRIVATE_EXPEDITED,
+ *          MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE,
  *          MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ).
  *
  * If this system call is not implemented, -ENOSYS is returned. If the
@@ -625,6 +627,8 @@ static int membarrier_get_registrations(void)
 SYSCALL_DEFINE3(membarrier, int, cmd, unsigned int, flags, int, cpu_id)
 {
 	switch (cmd) {
+	case MEMBARRIER_CMD_PRIVATE_EXPEDITED:
+	case MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE:
 	case MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ:
 		if (unlikely(flags && flags != MEMBARRIER_CMD_FLAG_CPU))
 			return -EINVAL;
-- 
2.49.0