From: Yan Zhai yan@cloudflare.com
[ Upstream commit 1a77557d48cff187a169c2aec01c0dd78a5e7e50 ]
When under heavy load, network processing can run CPU-bound for many tens of seconds. Even in preemptible kernels (non-RT kernel), this can block RCU Tasks grace periods, which can cause trace-event removal to take more than a minute, which is unacceptably long.
This commit therefore creates a new helper function that passes through both RCU and RCU-Tasks quiescent states every 100 milliseconds. This hard-coded value suffices for current workloads.
Suggested-by: Paul E. McKenney paulmck@kernel.org Reviewed-by: Jesper Dangaard Brouer hawk@kernel.org Signed-off-by: Yan Zhai yan@cloudflare.com Reviewed-by: Paul E. McKenney paulmck@kernel.org Acked-by: Jesper Dangaard Brouer hawk@kernel.org Link: https://lore.kernel.org/r/90431d46ee112d2b0af04dbfe936faaca11810a5.171087768... Signed-off-by: Jakub Kicinski kuba@kernel.org Stable-dep-of: d6dbbb11247c ("net: report RCU QS on threaded NAPI repolling") Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/rcupdate.h | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 44aab5c0bd2c1..9ad656b28847f 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -252,6 +252,37 @@ do { \ cond_resched(); \ } while (0)
+/** + * rcu_softirq_qs_periodic - Report RCU and RCU-Tasks quiescent states + * @old_ts: jiffies at start of processing. + * + * This helper is for long-running softirq handlers, such as NAPI threads in + * networking. The caller should initialize the variable passed in as @old_ts + * at the beginning of the softirq handler. When invoked frequently, this macro + * will invoke rcu_softirq_qs() every 100 milliseconds thereafter, which will + * provide both RCU and RCU-Tasks quiescent states. Note that this macro + * modifies its old_ts argument. + * + * Because regions of code that have disabled softirq act as RCU read-side + * critical sections, this macro should be invoked with softirq (and + * preemption) enabled. + * + * The macro is not needed when CONFIG_PREEMPT_RT is defined. RT kernels would + * have more chance to invoke schedule() calls and provide necessary quiescent + * states. As a contrast, calling cond_resched() only won't achieve the same + * effect because cond_resched() does not provide RCU-Tasks quiescent states. + */ +#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.