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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

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

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

> 
> 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>`
>  
> 
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