| Message ID | 4c3b0d3f32d3b18949d75b18e5e1d9f13a24f025.1710877680.git.yan@cloudflare.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | d6dbbb11247c71203785a2c9da474c36f4b19eae |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | Report RCU QS for busy network kthreads | expand |
On Tue, Mar 19, 2024 at 01:44:37PM -0700, Yan Zhai wrote: > NAPI threads can keep polling packets under load. Currently it is only > calling cond_resched() before repolling, but it is not sufficient to > clear out the holdout of RCU tasks, which prevent BPF tracing programs > from detaching for long period. This can be reproduced easily with > following set up: > > ip netns add test1 > ip netns add test2 > > ip -n test1 link add veth1 type veth peer name veth2 netns test2 > > ip -n test1 link set veth1 up > ip -n test1 link set lo up > ip -n test2 link set veth2 up > ip -n test2 link set lo up > > ip -n test1 addr add 192.168.1.2/31 dev veth1 > ip -n test1 addr add 1.1.1.1/32 dev lo > ip -n test2 addr add 192.168.1.3/31 dev veth2 > ip -n test2 addr add 2.2.2.2/31 dev lo > > ip -n test1 route add default via 192.168.1.3 > ip -n test2 route add default via 192.168.1.2 > > for i in `seq 10 210`; do > for j in `seq 10 210`; do > ip netns exec test2 iptables -I INPUT -s 3.3.$i.$j -p udp --dport 5201 > done > done > > ip netns exec test2 ethtool -K veth2 gro on > ip netns exec test2 bash -c 'echo 1 > /sys/class/net/veth2/threaded' > ip netns exec test1 ethtool -K veth1 tso off > > Then run an iperf3 client/server and a bpftrace script can trigger it: > > ip netns exec test2 iperf3 -s -B 2.2.2.2 >/dev/null& > ip netns exec test1 iperf3 -c 2.2.2.2 -B 1.1.1.1 -u -l 1500 -b 3g -t 100 >/dev/null& > bpftrace -e 'kfunc:__napi_poll{@=count();} interval:s:1{exit();}' > > Report RCU quiescent states periodically will resolve the issue. > > Fixes: 29863d41bb6e ("net: implement threaded-able napi poll loop support") > Reviewed-by: Jesper Dangaard Brouer <hawk@kernel.org> > Signed-off-by: Yan Zhai <yan@cloudflare.com> Acked-by: Paul E. McKenney <paulmck@kernel.org> > --- > v2->v3: abstracted the work into a RCU helper > v1->v2: moved rcu_softirq_qs out from bh critical section, and only > raise it after a second of repolling. Added some brief perf test result. > > v2: https://lore.kernel.org/bpf/ZeFPz4D121TgvCje@debian.debian/ > v1: https://lore.kernel.org/lkml/Zd4DXTyCf17lcTfq@debian.debian/#t > --- > net/core/dev.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/net/core/dev.c b/net/core/dev.c > index 303a6ff46e4e..9a67003e49db 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -6743,6 +6743,8 @@ static int napi_threaded_poll(void *data) > void *have; > > while (!napi_thread_wait(napi)) { > + unsigned long last_qs = jiffies; > + > for (;;) { > bool repoll = false; > > @@ -6767,6 +6769,7 @@ static int napi_threaded_poll(void *data) > if (!repoll) > break; > > + rcu_softirq_qs_periodic(last_qs); > cond_resched(); > } > } > -- > 2.30.2 > >
diff --git a/net/core/dev.c b/net/core/dev.c index 303a6ff46e4e..9a67003e49db 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -6743,6 +6743,8 @@ static int napi_threaded_poll(void *data) void *have; while (!napi_thread_wait(napi)) { + unsigned long last_qs = jiffies; + for (;;) { bool repoll = false; @@ -6767,6 +6769,7 @@ static int napi_threaded_poll(void *data) if (!repoll) break; + rcu_softirq_qs_periodic(last_qs); cond_resched(); } }
NAPI threads can keep polling packets under load. Currently it is only calling cond_resched() before repolling, but it is not sufficient to clear out the holdout of RCU tasks, which prevent BPF tracing programs from detaching for long period. This can be reproduced easily with following set up: ip netns add test1 ip netns add test2 ip -n test1 link add veth1 type veth peer name veth2 netns test2 ip -n test1 link set veth1 up ip -n test1 link set lo up ip -n test2 link set veth2 up ip -n test2 link set lo up ip -n test1 addr add 192.168.1.2/31 dev veth1 ip -n test1 addr add 1.1.1.1/32 dev lo ip -n test2 addr add 192.168.1.3/31 dev veth2 ip -n test2 addr add 2.2.2.2/31 dev lo ip -n test1 route add default via 192.168.1.3 ip -n test2 route add default via 192.168.1.2 for i in `seq 10 210`; do for j in `seq 10 210`; do ip netns exec test2 iptables -I INPUT -s 3.3.$i.$j -p udp --dport 5201 done done ip netns exec test2 ethtool -K veth2 gro on ip netns exec test2 bash -c 'echo 1 > /sys/class/net/veth2/threaded' ip netns exec test1 ethtool -K veth1 tso off Then run an iperf3 client/server and a bpftrace script can trigger it: ip netns exec test2 iperf3 -s -B 2.2.2.2 >/dev/null& ip netns exec test1 iperf3 -c 2.2.2.2 -B 1.1.1.1 -u -l 1500 -b 3g -t 100 >/dev/null& bpftrace -e 'kfunc:__napi_poll{@=count();} interval:s:1{exit();}' Report RCU quiescent states periodically will resolve the issue. Fixes: 29863d41bb6e ("net: implement threaded-able napi poll loop support") Reviewed-by: Jesper Dangaard Brouer <hawk@kernel.org> Signed-off-by: Yan Zhai <yan@cloudflare.com> --- v2->v3: abstracted the work into a RCU helper v1->v2: moved rcu_softirq_qs out from bh critical section, and only raise it after a second of repolling. Added some brief perf test result. v2: https://lore.kernel.org/bpf/ZeFPz4D121TgvCje@debian.debian/ v1: https://lore.kernel.org/lkml/Zd4DXTyCf17lcTfq@debian.debian/#t --- net/core/dev.c | 3 +++ 1 file changed, 3 insertions(+)