diff options
Diffstat (limited to 'Documentation/kernel-per-CPU-kthreads.txt')
| -rw-r--r-- | Documentation/kernel-per-CPU-kthreads.txt | 34 |
1 files changed, 21 insertions, 13 deletions
diff --git a/Documentation/kernel-per-CPU-kthreads.txt b/Documentation/kernel-per-CPU-kthreads.txt index f3cd299fcc41..f4cbfe0ba108 100644 --- a/Documentation/kernel-per-CPU-kthreads.txt +++ b/Documentation/kernel-per-CPU-kthreads.txt @@ -190,20 +190,24 @@ To reduce its OS jitter, do any of the following: on each CPU, including cs_dbs_timer() and od_dbs_timer(). WARNING: Please check your CPU specifications to make sure that this is safe on your particular system. - d. It is not possible to entirely get rid of OS jitter - from vmstat_update() on CONFIG_SMP=y systems, but you - can decrease its frequency by writing a large value - to /proc/sys/vm/stat_interval. The default value is - HZ, for an interval of one second. Of course, larger - values will make your virtual-memory statistics update - more slowly. Of course, you can also run your workload - at a real-time priority, thus preempting vmstat_update(), + d. 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 + decrease its frequency by writing a large value to + /proc/sys/vm/stat_interval. The default value is HZ, + for an interval of one second. Of course, larger values + will make your virtual-memory statistics update more + slowly. Of course, you can also run your workload at + a real-time priority, thus preempting vmstat_update(), but if your workload is CPU-bound, this is a bad idea. 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 + e. Boot with "elevator=noop" to avoid workqueue use by + the block layer. + f. 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 @@ -211,12 +215,12 @@ 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 + g. 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 + h. If running on PowerMAC, build your kernel with CONFIG_PMAC_RACKMETER=n to disable the CPU-meter, avoiding OS jitter from rackmeter_do_timer(). @@ -258,8 +262,12 @@ 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. Echo a zero to /proc/sys/kernel/watchdog to disable the +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/kernel-parameters.txt + and Documentation/watchdog/watchdog-parameters.txt. +3. Echo a zero to /proc/sys/kernel/watchdog to disable the watchdog timer. -3. Echo a large number of /proc/sys/kernel/watchdog_thresh in +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. |