netdev - [PATCH v3 10/13] task_isolation: net: don't flush backlog on CPUs running isolated tasks

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Date:   Thu, 9 Apr 2020 15:26:26 +0000
From:   Alex Belits <abelits@...vell.com>
To:     "frederic@...nel.org" <frederic@...nel.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>
CC:     Prasun Kapoor <pkapoor@...vell.com>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "will@...nel.org" <will@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: [PATCH v3 10/13] task_isolation: net: don't flush backlog on CPUs
 running isolated tasks

From: Yuri Norov <ynorov@...vell.com>

If CPU runs isolated task, there's no any backlog on it, and
so we don't need to flush it. Currently flush_all_backlogs()
enqueues corresponding work on all CPUs including ones that run
isolated tasks. It leads to breaking task isolation for nothing.

In this patch, backlog flushing is enqueued only on non-isolated CPUs.

Signed-off-by: Yuri Norov <ynorov@...vell.com>
[abelits@...vell.com: use safe task_isolation_on_cpu() implementation]
Signed-off-by: Alex Belits <abelits@...vell.com>
---
 net/core/dev.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index c6c985fe7b1b..353d2be39202 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -74,6 +74,7 @@
 #include <linux/cpu.h>
 #include <linux/types.h>
 #include <linux/kernel.h>
+#include <linux/isolation.h>
 #include <linux/hash.h>
 #include <linux/slab.h>
 #include <linux/sched.h>
@@ -5518,9 +5519,13 @@ static void flush_all_backlogs(void)
 
 	get_online_cpus();
 
-	for_each_online_cpu(cpu)
+	smp_rmb();
+	for_each_online_cpu(cpu) {
+		if (task_isolation_on_cpu(cpu))
+			continue;
 		queue_work_on(cpu, system_highpri_wq,
 			      per_cpu_ptr(&flush_works, cpu));
+	}
 
 	for_each_online_cpu(cpu)
 		flush_work(per_cpu_ptr(&flush_works, cpu));
-- 
2.20.1