diff options
Diffstat (limited to 'Documentation/admin-guide/kernel-per-CPU-kthreads.rst')
| -rw-r--r-- | Documentation/admin-guide/kernel-per-CPU-kthreads.rst | 44 |
1 files changed, 10 insertions, 34 deletions
diff --git a/Documentation/admin-guide/kernel-per-CPU-kthreads.rst b/Documentation/admin-guide/kernel-per-CPU-kthreads.rst index 21818aca4708..b6aeae3327ce 100644 --- a/Documentation/admin-guide/kernel-per-CPU-kthreads.rst +++ b/Documentation/admin-guide/kernel-per-CPU-kthreads.rst @@ -10,7 +10,7 @@ them to a "housekeeping" CPU dedicated to such work. References ========== -- Documentation/IRQ-affinity.txt: Binding interrupts to sets of CPUs. +- Documentation/core-api/irq/irq-affinity.rst: Binding interrupts to sets of CPUs. - Documentation/admin-guide/cgroup-v1: Using cgroups to bind tasks to sets of CPUs. @@ -25,7 +25,7 @@ References - In order to locate kernel-generated OS jitter on CPU N: - cd /sys/kernel/debug/tracing + cd /sys/kernel/tracing echo 1 > max_graph_depth # Increase the "1" for more detail echo function_graph > current_tracer # run workload @@ -208,7 +208,7 @@ Do at least one of the following: 2. Enable RCU to do its processing remotely via dyntick-idle by doing all of the following: - a. Build with CONFIG_NO_HZ=y and CONFIG_RCU_FAST_NO_HZ=y. + a. Build with CONFIG_NO_HZ=y. b. Ensure that the CPU goes idle frequently, allowing other CPUs to detect that it has passed through an RCU quiescent state. If the kernel is built with CONFIG_NO_HZ_FULL=y, @@ -243,13 +243,9 @@ To reduce its OS jitter, do any of the following: 3. Do any of the following needed to avoid jitter that your application cannot tolerate: - a. Build your kernel with CONFIG_SLUB=y rather than - CONFIG_SLAB=y, thus avoiding the slab allocator's periodic - use of each CPU's workqueues to run its cache_reap() - function. - b. Avoid using oprofile, thus avoiding OS jitter from + a. Avoid using oprofile, thus avoiding OS jitter from wq_sync_buffer(). - c. Limit your CPU frequency so that a CPU-frequency + b. Limit your CPU frequency so that a CPU-frequency governor is not required, possibly enlisting the aid of special heatsinks or other cooling technologies. If done correctly, and if you CPU architecture permits, you should @@ -259,7 +255,7 @@ To reduce its OS jitter, do any of the following: WARNING: Please check your CPU specifications to make sure that this is safe on your particular system. - d. As of v3.18, Christoph Lameter's on-demand vmstat workers + c. As of v3.18, Christoph Lameter's on-demand vmstat workers commit prevents OS jitter due to vmstat_update() on CONFIG_SMP=y systems. Before v3.18, is not possible to entirely get rid of the OS jitter, but you can @@ -273,8 +269,8 @@ To reduce its OS jitter, do any of the following: However, there is an RFC patch from Christoph Lameter (based on an earlier one from Gilad Ben-Yossef) that reduces or even eliminates vmstat overhead for some - workloads at https://lkml.org/lkml/2013/9/4/379. - e. If running on high-end powerpc servers, build with + workloads at https://lore.kernel.org/r/00000140e9dfd6bd-40db3d4f-c1be-434f-8132-7820f81bb586-000000@email.amazonses.com. + d. If running on high-end powerpc servers, build with CONFIG_PPC_RTAS_DAEMON=n. This prevents the RTAS daemon from running on each CPU every second or so. (This will require editing Kconfig files and will defeat @@ -282,12 +278,12 @@ To reduce its OS jitter, do any of the following: due to the rtas_event_scan() function. WARNING: Please check your CPU specifications to make sure that this is safe on your particular system. - f. If running on Cell Processor, build your kernel with + e. If running on Cell Processor, build your kernel with CBE_CPUFREQ_SPU_GOVERNOR=n to avoid OS jitter from spu_gov_work(). WARNING: Please check your CPU specifications to make sure that this is safe on your particular system. - g. If running on PowerMAC, build your kernel with + f. If running on PowerMAC, build your kernel with CONFIG_PMAC_RACKMETER=n to disable the CPU-meter, avoiding OS jitter from rackmeter_do_timer(). @@ -332,23 +328,3 @@ To reduce its OS jitter, do at least one of the following: kthreads from being created in the first place. However, please note that this will not eliminate OS jitter, but will instead shift it to RCU_SOFTIRQ. - -Name: - watchdog/%u - -Purpose: - Detect software lockups on each CPU. - -To reduce its OS jitter, do at least one of the following: - -1. Build with CONFIG_LOCKUP_DETECTOR=n, which will prevent these - kthreads from being created in the first place. -2. Boot with "nosoftlockup=0", which will also prevent these kthreads - from being created. Other related watchdog and softlockup boot - parameters may be found in Documentation/admin-guide/kernel-parameters.rst - and Documentation/watchdog/watchdog-parameters.rst. -3. Echo a zero to /proc/sys/kernel/watchdog to disable the - watchdog timer. -4. Echo a large number of /proc/sys/kernel/watchdog_thresh in - order to reduce the frequency of OS jitter due to the watchdog - timer down to a level that is acceptable for your workload. |