diff options
Diffstat (limited to 'features/rt/net-core-disable-NET_RX_BUSY_POLL-on-RT.patch')
| -rw-r--r-- | features/rt/net-core-disable-NET_RX_BUSY_POLL-on-RT.patch | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/features/rt/net-core-disable-NET_RX_BUSY_POLL-on-RT.patch b/features/rt/net-core-disable-NET_RX_BUSY_POLL-on-RT.patch new file mode 100644 index 00000000..4612f762 --- /dev/null +++ b/features/rt/net-core-disable-NET_RX_BUSY_POLL-on-RT.patch @@ -0,0 +1,43 @@ +From 116e028b98d7a297eccf815f0a734e80154b53c3 Mon Sep 17 00:00:00 2001 +From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +Date: Sat, 27 May 2017 19:02:06 +0200 +Subject: [PATCH 096/191] net/core: disable NET_RX_BUSY_POLL on RT + +napi_busy_loop() disables preemption and performs a NAPI poll. We can't acquire +sleeping locks with disabled preemption so we would have to work around this +and add explicit locking for synchronisation against ksoftirqd. +Without explicit synchronisation a low priority process would "own" the NAPI +state (by setting NAPIF_STATE_SCHED) and could be scheduled out (no +preempt_disable() and BH is preemptible on RT). +In case a network packages arrives then the interrupt handler would set +NAPIF_STATE_MISSED and the system would wait until the task owning the NAPI +would be scheduled in again. +Should a task with RT priority busy poll then it would consume the CPU instead +allowing tasks with lower priority to run. + +The NET_RX_BUSY_POLL is disabled by default (the system wide sysctls for +poll/read are set to zero) so disable NET_RX_BUSY_POLL on RT to avoid wrong +locking context on RT. Should this feature be considered useful on RT systems +then it could be enabled again with proper locking and synchronisation. + +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + net/Kconfig | 2 +- + 1 file changed, 1 insertion(+), 1 deletion(-) + +diff --git a/net/Kconfig b/net/Kconfig +index 8cea808ad9e8..32f101108361 100644 +--- a/net/Kconfig ++++ b/net/Kconfig +@@ -286,7 +286,7 @@ config CGROUP_NET_CLASSID + + config NET_RX_BUSY_POLL + bool +- default y ++ default y if !PREEMPT_RT + + config BQL + bool +-- +2.19.1 + |