Re: [Xen-devel] [RFC PATCH 2/5] XL: Increase event channels to support more vcpus

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Aug 28, 2017 at 05:11:27PM +0800, Lan, Tianyu wrote:
> On 8/25/2017 6:04 PM, Wei Liu wrote:
> > On Fri, Aug 25, 2017 at 10:57:26AM +0100, Roger Pau Monné wrote:
> > > On Fri, Aug 25, 2017 at 10:18:24AM +0100, Wei Liu wrote:
> > > > On Thu, Aug 24, 2017 at 10:52:17PM -0400, Lan Tianyu wrote:
> > > > > This patch is to increase event channels to support more vcpus in 
> > > > > single VM.
> > > > > 
> > > > > Signed-off-by: Lan Tianyu <tianyu.lan@xxxxxxxxx>
> > > > 
> > > > There is no need to bump the default. There is already a configuration
> > > > option called max_event_channel.
> > > 
> > > Maybe make this somehow based on the number of vCPUs assigned to the
> > > domain?
> > > 
> > > It's not very used-friendly to allow the creation of a domain with 256
> > > vCPUs for example that would then get stuck during boot.
> > > 
> > > Or at least check max_event_channel and the number of vCPUs and print
> > > a warning message to alert the user that things might go wrong with
> > > this configuration.
> > > 
> > 
> > The problem is number of vcpu is only one factor that would affect the
> > number of event channels needed.
> 
> How about producing a warning about event channel maybe not enough when vcpu
> number is >128 and still uses default max event channel number?
> 

Maybe. If you're going to do that, please:

1. provide the heuristic in a function so that it can be expand later.
2. make the message system administrator friendly, point them to the
   max_event_channels option.

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