diff options
Diffstat (limited to 'Documentation/kernel-per-CPU-kthreads.txt')
| -rw-r--r-- | Documentation/kernel-per-CPU-kthreads.txt | 31 |
1 files changed, 14 insertions, 17 deletions
diff --git a/Documentation/kernel-per-CPU-kthreads.txt b/Documentation/kernel-per-CPU-kthreads.txt index df31e30b6a02..2cb7dc5c0e0d 100644 --- a/Documentation/kernel-per-CPU-kthreads.txt +++ b/Documentation/kernel-per-CPU-kthreads.txt @@ -109,13 +109,12 @@ SCHED_SOFTIRQ: Do all of the following: on that CPU. If a thread that expects to run on the de-jittered CPU awakens, the scheduler will send an IPI that can result in a subsequent SCHED_SOFTIRQ. -2. Build with CONFIG_RCU_NOCB_CPU=y, CONFIG_RCU_NOCB_CPU_ALL=y, - CONFIG_NO_HZ_FULL=y, and, in addition, ensure that the CPU - to be de-jittered is marked as an adaptive-ticks CPU using the - "nohz_full=" boot parameter. This reduces the number of - scheduler-clock interrupts that the de-jittered CPU receives, - minimizing its chances of being selected to do the load balancing - work that runs in SCHED_SOFTIRQ context. +2. CONFIG_NO_HZ_FULL=y and ensure that the CPU to be de-jittered + is marked as an adaptive-ticks CPU using the "nohz_full=" + boot parameter. This reduces the number of scheduler-clock + interrupts that the de-jittered CPU receives, minimizing its + chances of being selected to do the load balancing work that + runs in SCHED_SOFTIRQ context. 3. To the extent possible, keep the CPU out of the kernel when it is non-idle, for example, by avoiding system calls and by forcing both kernel threads and interrupts to execute elsewhere. @@ -135,11 +134,10 @@ HRTIMER_SOFTIRQ: Do all of the following: RCU_SOFTIRQ: Do at least one of the following: 1. Offload callbacks and keep the CPU in either dyntick-idle or adaptive-ticks state by doing all of the following: - a. Build with CONFIG_RCU_NOCB_CPU=y, CONFIG_RCU_NOCB_CPU_ALL=y, - CONFIG_NO_HZ_FULL=y, and, in addition ensure that the CPU - to be de-jittered is marked as an adaptive-ticks CPU using - the "nohz_full=" boot parameter. Bind the rcuo kthreads - to housekeeping CPUs, which can tolerate OS jitter. + a. CONFIG_NO_HZ_FULL=y and ensure that the CPU to be + de-jittered is marked as an adaptive-ticks CPU using the + "nohz_full=" boot parameter. Bind the rcuo kthreads to + housekeeping CPUs, which can tolerate OS jitter. b. To the extent possible, keep the CPU out of the kernel when it is non-idle, for example, by avoiding system calls and by forcing both kernel threads and interrupts @@ -236,11 +234,10 @@ To reduce its OS jitter, do at least one of the following: is feasible only if your workload never requires RCU priority boosting, for example, if you ensure frequent idle time on all CPUs that might execute within the kernel. -3. Build with CONFIG_RCU_NOCB_CPU=y and CONFIG_RCU_NOCB_CPU_ALL=y, - which offloads all RCU callbacks to kthreads that can be moved - off of CPUs susceptible to OS jitter. This approach prevents the - rcuc/%u kthreads from having any work to do, so that they are - never awakened. +3. Build with CONFIG_RCU_NOCB_CPU=y and boot with the rcu_nocbs= + boot parameter offloading RCU callbacks from all CPUs susceptible + to OS jitter. This approach prevents the rcuc/%u kthreads from + having any work to do, so that they are never awakened. 4. Ensure that the CPU never enters the kernel, and, in particular, avoid initiating any CPU hotplug operations on this CPU. This is another way of preventing any callbacks from being queued on the |