From 41abcf321d447b9987f6b7d1a9bb65831e786daf Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 11 Dec 2015 16:18:22 -0800 Subject: documentation: Add real-time requirements from CPU-bound workloads This commit records RCU's responsibility to avoid degrading latencies of CPUs running tight loops within properly configured workloads, both in kernel and in userspace. Signed-off-by: Paul E. McKenney --- Documentation/RCU/Design/Requirements/Requirements.html | 10 +++++++++- Documentation/RCU/Design/Requirements/Requirements.htmlx | 8 ++++++++ 2 files changed, 17 insertions(+), 1 deletion(-) (limited to 'Documentation/RCU') diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html index a725f9900ec8..3004baa71bcc 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.html +++ b/Documentation/RCU/Design/Requirements/Requirements.html @@ -1,5 +1,5 @@ - + @@ -2170,6 +2170,14 @@ up to and including systems with 4096 CPUs. This real-time requirement motivated the grace-period kthread, which also simplified handling of a number of race conditions. +

+RCU must avoid degrading real-time response for CPU-bound threads, whether +executing in usermode (which is one use case for +CONFIG_NO_HZ_FULL=y) or in the kernel. +That said, CPU-bound loops in the kernel must execute +cond_resched_rcu_qs() at least once per few tens of milliseconds +in order to avoid receiving an IPI from RCU. +

Finally, RCU's status as a synchronization primitive means that any RCU failure can result in arbitrary memory corruption that can be diff --git a/Documentation/RCU/Design/Requirements/Requirements.htmlx b/Documentation/RCU/Design/Requirements/Requirements.htmlx index 3a97ba490c42..61caffc86823 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.htmlx +++ b/Documentation/RCU/Design/Requirements/Requirements.htmlx @@ -2337,6 +2337,14 @@ up to and including systems with 4096 CPUs. This real-time requirement motivated the grace-period kthread, which also simplified handling of a number of race conditions. +

+RCU must avoid degrading real-time response for CPU-bound threads, whether +executing in usermode (which is one use case for +CONFIG_NO_HZ_FULL=y) or in the kernel. +That said, CPU-bound loops in the kernel must execute +cond_resched_rcu_qs() at least once per few tens of milliseconds +in order to avoid receiving an IPI from RCU. +

Finally, RCU's status as a synchronization primitive means that any RCU failure can result in arbitrary memory corruption that can be -- cgit v1.2.3