linux-kernel - [Patch v3 3/3] net: Restrict receive packets queuing to housekeeping CPUs

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Message-Id: <20200623192331.215557-4-nitesh@redhat.com>
Date:   Tue, 23 Jun 2020 15:23:31 -0400
From:   Nitesh Narayan Lal <nitesh@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        frederic@...nel.org, mtosatti@...hat.com, juri.lelli@...hat.com,
        abelits@...vell.com, bhelgaas@...gle.com,
        linux-pci@...r.kernel.org, rostedt@...dmis.org, mingo@...nel.org,
        peterz@...radead.org, tglx@...utronix.de, davem@...emloft.net,
        akpm@...ux-foundation.org, sfr@...b.auug.org.au,
        stephen@...workplumber.org, rppt@...ux.vnet.ibm.com
Subject: [Patch v3 3/3] net: Restrict receive packets queuing to housekeeping CPUs

From: Alex Belits <abelits@...vell.com>

With the existing implementation of store_rps_map(), packets are queued
in the receive path on the backlog queues of other CPUs irrespective of
whether they are isolated or not. This could add a latency overhead to
any RT workload that is running on the same CPU.

Ensure that store_rps_map() only uses available housekeeping CPUs for
storing the rps_map.

Signed-off-by: Alex Belits <abelits@...vell.com>
Signed-off-by: Nitesh Narayan Lal <nitesh@...hat.com>
---
 net/core/net-sysfs.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index e353b822bb15..677868fea316 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -11,6 +11,7 @@
 #include <linux/if_arp.h>
 #include <linux/slab.h>
 #include <linux/sched/signal.h>
+#include <linux/sched/isolation.h>
 #include <linux/nsproxy.h>
 #include <net/sock.h>
 #include <net/net_namespace.h>
@@ -741,7 +742,7 @@ static ssize_t store_rps_map(struct netdev_rx_queue *queue,
 {
 	struct rps_map *old_map, *map;
 	cpumask_var_t mask;
-	int err, cpu, i;
+	int err, cpu, i, hk_flags;
 	static DEFINE_MUTEX(rps_map_mutex);
 
 	if (!capable(CAP_NET_ADMIN))
@@ -756,6 +757,13 @@ static ssize_t store_rps_map(struct netdev_rx_queue *queue,
 		return err;
 	}
 
+	hk_flags = HK_FLAG_DOMAIN | HK_FLAG_WQ;
+	cpumask_and(mask, mask, housekeeping_cpumask(hk_flags));
+	if (cpumask_empty(mask)) {
+		free_cpumask_var(mask);
+		return -EINVAL;
+	}
+
 	map = kzalloc(max_t(unsigned int,
 			    RPS_MAP_SIZE(cpumask_weight(mask)), L1_CACHE_BYTES),
 		      GFP_KERNEL);
-- 
2.18.4