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-rw-r--r--meta-agl-core/recipes-kernel/linux/linux/net-sch_generic-Use-pfifo_fast-as-fallback-scheduler.patch75
1 files changed, 75 insertions, 0 deletions
diff --git a/meta-agl-core/recipes-kernel/linux/linux/net-sch_generic-Use-pfifo_fast-as-fallback-scheduler.patch b/meta-agl-core/recipes-kernel/linux/linux/net-sch_generic-Use-pfifo_fast-as-fallback-scheduler.patch
new file mode 100644
index 000000000..37ace5a58
--- /dev/null
+++ b/meta-agl-core/recipes-kernel/linux/linux/net-sch_generic-Use-pfifo_fast-as-fallback-scheduler.patch
@@ -0,0 +1,75 @@
+From 546b85bb0aadb5a928b49b53dc02911996169c0b Mon Sep 17 00:00:00 2001
+From: Vincent Prince <vincent.prince.fr@gmail.com>
+Date: Wed, 23 Oct 2019 15:44:20 +0200
+Subject: [PATCH] net: sch_generic: Use pfifo_fast as fallback scheduler for
+ CAN hardware
+
+There is networking hardware that isn't based on Ethernet for layers 1 and 2.
+
+For example CAN.
+
+CAN is a multi-master serial bus standard for connecting Electronic Control
+Units [ECUs] also known as nodes. A frame on the CAN bus carries up to 8 bytes
+of payload. Frame corruption is detected by a CRC. However frame loss due to
+corruption is possible, but a quite unusual phenomenon.
+
+While fq_codel works great for TCP/IP, it doesn't for CAN. There are a lot of
+legacy protocols on top of CAN, which are not build with flow control or high
+CAN frame drop rates in mind.
+
+When using fq_codel, as soon as the queue reaches a certain delay based length,
+skbs from the head of the queue are silently dropped. Silently meaning that the
+user space using a send() or similar syscall doesn't get an error. However
+TCP's flow control algorithm will detect dropped packages and adjust the
+bandwidth accordingly.
+
+When using fq_codel and sending raw frames over CAN, which is the common use
+case, the user space thinks the package has been sent without problems, because
+send() returned without an error. pfifo_fast will drop skbs, if the queue
+length exceeds the maximum. But with this scheduler the skbs at the tail are
+dropped, an error (-ENOBUFS) is propagated to user space. So that the user
+space can slow down the package generation.
+
+On distributions, where fq_codel is made default via CONFIG_DEFAULT_NET_SCH
+during compile time, or set default during runtime with sysctl
+net.core.default_qdisc (see [1]), we get a bad user experience. In my test case
+with pfifo_fast, I can transfer thousands of million CAN frames without a frame
+drop. On the other hand with fq_codel there is more then one lost CAN frame per
+thousand frames.
+
+As pointed out fq_codel is not suited for CAN hardware, so this patch changes
+attach_one_default_qdisc() to use pfifo_fast for "ARPHRD_CAN" network devices.
+
+During transition of a netdev from down to up state the default queuing
+discipline is attached by attach_default_qdiscs() with the help of
+attach_one_default_qdisc(). This patch modifies attach_one_default_qdisc() to
+attach the pfifo_fast (pfifo_fast_ops) if the network device type is
+"ARPHRD_CAN".
+
+[1] https://github.com/systemd/systemd/issues/9194
+
+Suggested-by: Marc Kleine-Budde <mkl@pengutronix.de>
+Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
+Signed-off-by: Vincent Prince <vincent.prince.fr@gmail.com>
+Acked-by: Dave Taht <dave.taht@gmail.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ net/sched/sch_generic.c | 2 ++
+ 1 file changed, 2 insertions(+)
+
+diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
+index ed5b0e9fd395..4c5dfcb01e00 100644
+--- a/net/sched/sch_generic.c
++++ b/net/sched/sch_generic.c
+@@ -1038,6 +1038,8 @@ static void attach_one_default_qdisc(struct net_device *dev,
+
+ if (dev->priv_flags & IFF_NO_QUEUE)
+ ops = &noqueue_qdisc_ops;
++ else if(dev->type == ARPHRD_CAN)
++ ops = &pfifo_fast_ops;
+
+ qdisc = qdisc_create_dflt(dev_queue, ops, TC_H_ROOT, NULL);
+ if (!qdisc) {
+--
+2.25.0
+