linux-kernel - [tip: perf/urgent] perf: Optimize perf_pmu_migrate

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <168077550562.404.4256750619103519881.tip-bot2@tip-bot2>
Date:   Thu, 06 Apr 2023 10:05:05 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: perf/urgent] perf: Optimize perf_pmu_migrate_context()

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     b168098912926236bbeebaf7795eb7aab76d2b45
Gitweb:        https://git.kernel.org/tip/b168098912926236bbeebaf7795eb7aab76d2b45
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Mon, 03 Apr 2023 11:08:58 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 05 Apr 2023 09:58:46 +02:00

perf: Optimize perf_pmu_migrate_context()

Thomas reported that offlining CPUs spends a lot of time in
synchronize_rcu() as called from perf_pmu_migrate_context() even though
he's not actually using uncore events.

Turns out, the thing is unconditionally waiting for RCU, even if there's
no actual events to migrate.

Fixes: 0cda4c023132 ("perf: Introduce perf_pmu_migrate_context()")
Reported-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Paul E. McKenney <paulmck@...nel.org>
Link: https://lkml.kernel.org/r/20230403090858.GT4253@hirez.programming.kicks-ass.net
---
 kernel/events/core.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index fb3e436..115320f 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -12893,12 +12893,14 @@ void perf_pmu_migrate_context(struct pmu *pmu, int src_cpu, int dst_cpu)
 	__perf_pmu_remove(src_ctx, src_cpu, pmu, &src_ctx->pinned_groups, &events);
 	__perf_pmu_remove(src_ctx, src_cpu, pmu, &src_ctx->flexible_groups, &events);
 
-	/*
-	 * Wait for the events to quiesce before re-instating them.
-	 */
-	synchronize_rcu();
+	if (!list_empty(&events)) {
+		/*
+		 * Wait for the events to quiesce before re-instating them.
+		 */
+		synchronize_rcu();
 
-	__perf_pmu_install(dst_ctx, dst_cpu, pmu, &events);
+		__perf_pmu_install(dst_ctx, dst_cpu, pmu, &events);
+	}
 
 	mutex_unlock(&dst_ctx->mutex);
 	mutex_unlock(&src_ctx->mutex);