Add comment on cpumask not working with a CPU count > 32

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --git a/HOWTO b/HOWTO
index 4298f3245daed2b850cc0bcf3077fad48f8404e5..5a55c1a21b574a3adba1aa52f4f0fee6f42458c7 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -583,7 +583,10 @@ cpumask=int        Set the CPU affinity of this job. The parameter given is a
                the allowed CPUs to be 1 and 5, you would pass the decimal
                value of (1 << 1 | 1 << 5), or 34. See man
                sched_setaffinity(2). This may not work on all supported
                the allowed CPUs to be 1 and 5, you would pass the decimal
                value of (1 << 1 | 1 << 5), or 34. See man
                sched_setaffinity(2). This may not work on all supported

-               operating systems or kernel versions.
+               operating systems or kernel versions. This option doesn't
+               work well for a higher CPU count than what you can store in
+               an integer mask, so it can only control cpus 1-32. For
+               boxes with larger CPU counts, use cpus_allowed.

 
 cpus_allowed=str Controls the same options as cpumask, but it allows a text
                setting of the permitted CPUs instead. So to use CPUs 1 and
 
 cpus_allowed=str Controls the same options as cpumask, but it allows a text
                setting of the permitted CPUs instead. So to use CPUs 1 and