From: Yan Zhai <yan@cloudflare.com>
To: netdev@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>,
"Eric Dumazet" <edumazet@google.com>,
"Jakub Kicinski" <kuba@kernel.org>,
"Paolo Abeni" <pabeni@redhat.com>,
"Jiri Pirko" <jiri@resnulli.us>,
"Simon Horman" <horms@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Lorenzo Bianconi" <lorenzo@kernel.org>,
"Coco Li" <lixiaoyan@google.com>, "Wei Wang" <weiwan@google.com>,
"Alexander Duyck" <alexanderduyck@fb.com>,
"Hannes Frederic Sowa" <hannes@stressinduktion.org>,
linux-kernel@vger.kernel.org, rcu@vger.kernel.org,
bpf@vger.kernel.org, kernel-team@cloudflare.com,
"Joel Fernandes" <joel@joelfernandes.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
"Toke Høiland-Jørgensen" <toke@redhat.com>,
"Alexei Starovoitov" <alexei.starovoitov@gmail.com>,
"Steven Rostedt" <rostedt@goodmis.org>,
mark.rutland@arm.com, "Jesper Dangaard Brouer" <hawk@kernel.org>
Subject: [PATCH v4 net 1/3] rcu: add a helper to report consolidated flavor QS
Date: Fri, 15 Mar 2024 12:55:03 -0700 [thread overview]
Message-ID: <491d3af6c7d66dfb3b60b2f210f38e843dfe6ed2.1710525524.git.yan@cloudflare.com> (raw)
In-Reply-To: <cover.1710525524.git.yan@cloudflare.com>
There are several scenario in network processing that can run
extensively under heavy traffic. In such situation, RCU synchronization
might not observe desired quiescent states for indefinitely long period.
Create a helper to safely raise the desired RCU quiescent states for
such scenario.
Currently the frequency is locked at HZ/10, i.e. 100ms, which is
sufficient to address existing problems around RCU tasks. It's unclear
yet if there is any future scenario for it to be further tuned down.
Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Jesper Dangaard Brouer <hawk@kernel.org>
Signed-off-by: Yan Zhai <yan@cloudflare.com>
---
v3->v4: comment fixup
---
include/linux/rcupdate.h | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 0746b1b0b663..da224706323e 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -247,6 +247,30 @@ do { \
cond_resched(); \
} while (0)
+/**
+ * rcu_softirq_qs_periodic - Periodically report consolidated quiescent states
+ * @old_ts: last jiffies when QS was reported. Might be modified in the macro.
+ *
+ * This helper is for network processing in non-RT kernels, where there could
+ * be busy polling threads that block RCU synchronization indefinitely. In
+ * such context, simply calling cond_resched is insufficient, so give it a
+ * stronger push to eliminate all potential blockage of all RCU types.
+ *
+ * NOTE: unless absolutely sure, this helper should in general be called
+ * outside of bh lock section to avoid reporting a surprising QS to updaters,
+ * who could be expecting RCU read critical section to end at local_bh_enable().
+ */
+#define rcu_softirq_qs_periodic(old_ts) \
+do { \
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT) && \
+ time_after(jiffies, (old_ts) + HZ / 10)) { \
+ preempt_disable(); \
+ rcu_softirq_qs(); \
+ preempt_enable(); \
+ (old_ts) = jiffies; \
+ } \
+} while (0)
+
/*
* Infrastructure to implement the synchronize_() primitives in
* TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
--
2.30.2
next prev parent reply other threads:[~2024-03-15 19:55 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-15 19:55 [PATCH v4 net 0/3] Report RCU QS for busy network kthreads Yan Zhai
2024-03-15 19:55 ` Yan Zhai [this message]
2024-03-16 5:40 ` [PATCH v4 net 1/3] rcu: add a helper to report consolidated flavor QS Paul E. McKenney
2024-03-18 10:58 ` Mark Rutland
2024-03-19 2:32 ` Yan Zhai
2024-03-19 2:39 ` Yan Zhai
2024-03-19 1:26 ` Yan Zhai
2024-03-15 19:55 ` [PATCH v4 net 2/3] net: report RCU QS on threaded NAPI repolling Yan Zhai
2024-03-15 19:55 ` [PATCH v4 net 3/3] bpf: report RCU QS in cpumap kthread Yan Zhai
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