diff options
Diffstat (limited to 'debian/patches-rt/net_disable_NET_RX_BUSY_POLL.patch')
| -rw-r--r-- | debian/patches-rt/net_disable_NET_RX_BUSY_POLL.patch | 31 |
1 files changed, 20 insertions, 11 deletions
diff --git a/debian/patches-rt/net_disable_NET_RX_BUSY_POLL.patch b/debian/patches-rt/net_disable_NET_RX_BUSY_POLL.patch index f59cd5be4..650b6c7e8 100644 --- a/debian/patches-rt/net_disable_NET_RX_BUSY_POLL.patch +++ b/debian/patches-rt/net_disable_NET_RX_BUSY_POLL.patch @@ -1,15 +1,24 @@ From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Date: Sat, 27 May 2017 19:02:06 +0200 -Subject: net/core: disable NET_RX_BUSY_POLL -Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.2/older/patches-5.2.17-rt9.tar.xz +Subject: net/core: disable NET_RX_BUSY_POLL on RT +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.4/older/patches-5.4.3-rt1.tar.xz -sk_busy_loop() does preempt_disable() followed by a few operations which can -take sleeping locks and may get long. -I _think_ that we could use preempt_disable_nort() (in sk_busy_loop()) instead -but after a successfull cmpxchg(&napi->state, …) we would gain the ressource -and could be scheduled out. At this point nobody knows who (which context) owns -it and so it could take a while until the state is realeased and napi_poll() -could be invoked again. +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> --- @@ -18,12 +27,12 @@ Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- a/net/Kconfig +++ b/net/Kconfig -@@ -280,7 +280,7 @@ config CGROUP_NET_CLASSID +@@ -278,7 +278,7 @@ config CGROUP_NET_CLASSID config NET_RX_BUSY_POLL bool - default y -+ default y if !PREEMPT_RT_FULL ++ default y if !PREEMPT_RT config BQL bool |