Re: [PATCH][4.15] Performance regression due to XSA-336

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.03.2021 12:53, Ian Jackson wrote:
> Jan Beulich writes ("Re: [PATCH][4.15] Performance regression due to 
> XSA-336"):
>> While the change is more intrusive than one would like at this point, an
>> up-to-40% regression imo makes this at least a change to be considered
>> for 4.15. I will admit though that before next week I won't get around
>> to look at this in any more detail than just having read through this
>> cover letter. But perhaps someone else might find time earlier.
> 
> As I understand it:
> 
> This amounts to a request to consider a release ack for "x86/vpt:
> Replace per-guest pt_migrate lock with per pt lock".

Or, as already suggested by Roger, perhaps something simpler. First of
all I wanted you to be aware.

> That patch fixes a regression due to XSA-336.  XSA-336 affected many
> versions of Xen.  Therefore this is not a regression between 4.14 and
> 4.15; rather it's a regresion from pre-XSA-336 to post-XSA-336.
> 
> I looked at the patch and I am really not comfortable with that kind
> of change at this stage of the release.
> 
> So I'm afraid the answer is no, unless I have misunderstood something.

Understood.

Jan