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documentation: Update based on on-demand vmstat workers
Now that the on-demand vmstat workers commit is in mainline, it is possible to eliminate vmstat_update()-induced OS jitter. This commit updates the documentation accordingly. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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@ -190,14 +190,16 @@ To reduce its OS jitter, do any of the following:
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on each CPU, including cs_dbs_timer() and od_dbs_timer().
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WARNING: Please check your CPU specifications to
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make sure that this is safe on your particular system.
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d. It is not possible to entirely get rid of OS jitter
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from vmstat_update() on CONFIG_SMP=y systems, but you
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can decrease its frequency by writing a large value
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to /proc/sys/vm/stat_interval. The default value is
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HZ, for an interval of one second. Of course, larger
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values will make your virtual-memory statistics update
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more slowly. Of course, you can also run your workload
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at a real-time priority, thus preempting vmstat_update(),
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d. As of v3.18, Christoph Lameter's on-demand vmstat workers
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commit prevents OS jitter due to vmstat_update() on
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CONFIG_SMP=y systems. Before v3.18, is not possible
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to entirely get rid of the OS jitter, but you can
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decrease its frequency by writing a large value to
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/proc/sys/vm/stat_interval. The default value is HZ,
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for an interval of one second. Of course, larger values
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will make your virtual-memory statistics update more
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slowly. Of course, you can also run your workload at
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a real-time priority, thus preempting vmstat_update(),
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but if your workload is CPU-bound, this is a bad idea.
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However, there is an RFC patch from Christoph Lameter
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(based on an earlier one from Gilad Ben-Yossef) that
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