Re: [PATCH 1/2] credit: Limit load balancing to once per millisecond

[George Dunlap <george.dunlap@xxxxxxxxx>]

On Tue, Jul 4, 2023 at 6:34 PM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:

On 30/06/2023 12:37 pm, George Dunlap wrote:
>
>  docs/misc/xen-command-line.pandoc |  6 +++++
>  xen/common/sched/credit.c         | 40 ++++++++++++++++++++++++++-----
>  xen/include/public/sysctl.h       |  6 +++++

Given this filelist, why the sysctl change?

There's no logic to drive this parameter in the xc/libxl param get/set.

The only two in-tree users I can see are xenpm, along with an
unconditional print to stderr saying it's deprecated and to use xl, and xl.

Yes.  I think unless someone objects then, I'll drop the sysctl interface from this patch, and add it in a follow-up patch (perhaps at a later date, depending on how much time I have this week).

 

> diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc
> index 4060ebdc5d..369557020f 100644
> --- a/docs/misc/xen-command-line.pandoc
> +++ b/docs/misc/xen-command-line.pandoc
> @@ -1856,6 +1856,12 @@ By default, Xen will use the INVPCID instruction for TLB management if
>  it is available.  This option can be used to cause Xen to fall back to
>  older mechanisms, which are generally slower.
> 
> +### load-balance-ratelimit
> +> `= <integer>`
> +
> +The minimum interval between load balancing events on a given pcpu.
> +At the moment only credit honors this parameter.

So this is intended to be a global scheduler parameter?

Yes; nearly every scheduler does load balancing, and so any scheduler may need this sort of limitation at some point.  It doesn't make sense to have separate, nearly identical parameters for each scheduler.  At some point this should probably be implemented for credit2, although perhaps with a different default.

 

Ack on the two style comments.

 -George