Re: [PATCH v4 6/6] introduce simple linear scan rate limiting mechanism

[Peter Xu]

On Mon, Nov 30, 2020 at 11:11:00AM +0300, Andrey Gruzdev wrote:
> On 28.11.2020 01:28, Peter Xu wrote:
> > On Thu, Nov 26, 2020 at 06:17:34PM +0300, Andrey Gruzdev wrote:
> > > Since reading UFFD events and saving paged data are performed
> > > from the same thread, write fault latencies are sensitive to
> > > migration stream stalls. Limiting total page saving rate is a
> > > method to reduce amount of noticiable fault resolution latencies.
> > > 
> > > Migration bandwidth limiting is achieved via noticing cases of
> > > out-of-threshold write fault latencies and temporarily disabling
> > > (strictly speaking, severely throttling) saving non-faulting pages.
> > 
> > So have you done any measurements out of it, as we've talked in previous
> > version?  Thanks,
> > 
> 
> Sorry, not done yet.

So do you still plan to? :)

And if not, could you describe the rational behind this patch?  For example,
what's the problem behind (e.g., guest hangs for xxx seconds, maybe?) and
what's the outcome (guest doesn't hang any more)?

Thanks,

-- 
Peter Xu