[PATCH] docs: Document scheduler-related Xen command-line options

[PATCH] docs: Document scheduler-related Xen command-line options

[George Dunlap]

# HG changeset patch
# User George Dunlap <george.dunlap@eu.citrix.com>
# Date 1348499935 -3600
# Node ID 7e332fd064fac8d9d1cea904d5236c8d74389194
# Parent  7b045d43e59dcb42340097058502bf456e151180
docs: Document scheduler-related Xen command-line options

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>

diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -732,12 +732,34 @@ Choose the default scheduler.
 ### sched\_credit\_tslice\_ms
 > `= <integer>`
 
+Set the timeslice of the credit1 scheduler, in milliseconds.  The
+default is 30ms.  Reasonable values may include 10, 5, or even 1 for
+very latency-sensitive workloads.
+
 ### sched\_ratelimit\_us
 > `= <integer>`
 
+In order to limit the rate of context switching, set the minimum
+amount of time that a vcpu can be scheduled for before preempting it,
+in microseconds.  The default is 1000us (1ms).  Setting this to 0
+disables it altogether.
+
 ### sched\_smt\_power\_savings
 > `= <boolean>`
 
+Normally Xen will try to maximize performance and cache utilization by
+spreading out vcpus across as many different divisions as possible
+(i.e, numa nodes, sockets, cores threads, &c).  This often maximizes
+throughput, but also maximizes energy usage, since it reduces the
+depth to which a processor can sleep.
+
+This option inverts the logic, so that the scheduler in effect tries
+to keep the vcpus on the smallest amount of silicon possible; i.e.,
+first fill up sibling threads, then sibling cores, then sibling
+sockets, &c.  This will reduce performance somewhat, particularly on
+systems with hyperthreading enabled, but should reduce power by
+enabling more sockets and cores to go into deeper sleep states.
+
 ### serial\_tx\_buffer
 > `= <size>`

Re: [PATCH] docs: Document scheduler-related Xen command-line options

[Ian Campbell]

On Mon, 2012-09-24 at 16:19 +0100, George Dunlap wrote:
> # HG changeset patch
> # User George Dunlap <george.dunlap@eu.citrix.com>
> # Date 1348499935 -3600
> # Node ID 7e332fd064fac8d9d1cea904d5236c8d74389194
> # Parent  7b045d43e59dcb42340097058502bf456e151180
> docs: Document scheduler-related Xen command-line options
> 
> Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>

Acked-by: Ian Campbell <ian.campbell@citrix.com>

> 
> diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown
> --- a/docs/misc/xen-command-line.markdown
> +++ b/docs/misc/xen-command-line.markdown
> @@ -732,12 +732,34 @@ Choose the default scheduler.
>  ### sched\_credit\_tslice\_ms
>  > `= <integer>`
>  
> +Set the timeslice of the credit1 scheduler, in milliseconds.  The
> +default is 30ms.  Reasonable values may include 10, 5, or even 1 for
> +very latency-sensitive workloads.
> +
>  ### sched\_ratelimit\_us
>  > `= <integer>`
>  
> +In order to limit the rate of context switching, set the minimum
> +amount of time that a vcpu can be scheduled for before preempting it,
> +in microseconds.  The default is 1000us (1ms).  Setting this to 0
> +disables it altogether.
> +
>  ### sched\_smt\_power\_savings
>  > `= <boolean>`
>  
> +Normally Xen will try to maximize performance and cache utilization by
> +spreading out vcpus across as many different divisions as possible
> +(i.e, numa nodes, sockets, cores threads, &c).  This often maximizes
> +throughput, but also maximizes energy usage, since it reduces the
> +depth to which a processor can sleep.
> +
> +This option inverts the logic, so that the scheduler in effect tries
> +to keep the vcpus on the smallest amount of silicon possible; i.e.,
> +first fill up sibling threads, then sibling cores, then sibling
> +sockets, &c.  This will reduce performance somewhat, particularly on
> +systems with hyperthreading enabled, but should reduce power by
> +enabling more sockets and cores to go into deeper sleep states.
> +
>  ### serial\_tx\_buffer
>  > `= <size>`
>  
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel

Re: [PATCH] docs: Document scheduler-related Xen command-line options

[Ian Jackson]

George Dunlap writes ("[Xen-devel] [PATCH] docs: Document scheduler-related Xen command-line options"):
> docs: Document scheduler-related Xen command-line options

Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

Ian.