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xl: update the manpage about "cpus=" and NUMA node-affinity
Since d06b1bf169 ('libxl: automatic placement
deals with node-affinity') it is no longer true that, if no "cpus=" option
is specified, xl picks up some pCPUs by default and pin the domain there.
In fact, it is the NUMA node-affinity that is affected by automatic
placement, not vCPU to pCPU pinning.
Update the xl config file documenation accordingly, as it seems to have
been forgotten at that time.
Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
This commit is contained in:
Dario Faggioli authored and Ian Campbell committed
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@@ -104,8 +104,8 @@ created online and the remainder will be offline.
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=item B<cpus="CPU-LIST">
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List of which cpus the guest is allowed to use. By default xl will pick
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some cpus on its own (see below). A C<CPU-LIST> may be specified as follows:
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List of which cpus the guest is allowed to use. Default is no pinning at
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all (more on this below). A C<CPU-LIST> may be specified as follows:
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=over 4
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@@ -125,11 +125,19 @@ run on cpu #3 of the host.
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=back
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If this option is not specified, libxl automatically tries to place the new
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domain on the host's NUMA nodes (provided the host has more than one NUMA
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node) by pinning it to the cpus of those nodes. A heuristic approach is
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utilized with the goals of maximizing performance for the domain and, at
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the same time, achieving efficient utilization of the host's CPUs and RAM.
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If this option is not specified, no vcpu to cpu pinning is established,
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and the vcpus of the guest can run on all the cpus of the host.
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If we are on a NUMA machine (i.e., if the host has more than one NUMA
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node) and this option is not specified, libxl automatically tries to
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place the guest on the least possible number of nodes. That, however,
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will not affect vcpu pinning, so the guest will still be able to run on
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all the cpus, it will just prefer the ones from the node it has been
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placed on. A heuristic approach is used for choosing the best node (or
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set of nodes), with the goals of maximizing performance for the guest
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and, at the same time, achieving efficient utilization of host cpus
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and memory. See F<docs/misc/xl-numa-placement.markdown> for more
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details.
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=back
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