Re: [Xen-devel] [PATCH v2] x86/mm: also flush TLB when putting writable foreign page reference

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 27.04.17 at 11:51, <tim@xxxxxxx> wrote:
> At 03:23 -0600 on 27 Apr (1493263380), Jan Beulich wrote:
>> ... it wouldn't better be the other way around: We use the patch
>> in its current (or even v1) form, and try to do something about
>> performance only if we really find a case where it matters. To be
>> honest, I'm not even sure how I could meaningfully measure the
>> impact here: Simply counting how many extra flushes there would
>> end up being wouldn't seem all that useful, and whether there
>> would be any measurable difference in the overall execution time
>> of e.g. domain creation I would highly doubt (but if it's that what
>> you're after, I could certainly collect a few numbers).
> 
> I think that would be a good idea, just as a sanity-check.

As it turns out there is a measurable effect: xc_dom_boot_image()
for a 4Gb PV guest takes about 70% longer now. Otoh it is itself
responsible for less than 10% of the overall time libxl__build_dom()
takes, and that in turn is only a pretty small portion of the overall
"xl create".

Jan


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