Re: [Xen-devel] [PATCH v6 4/7] x86: collect CQM information from all sockets

["Xu, Dongxiao" <dongxiao.xu@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Tuesday, January 28, 2014 11:04 PM
> To: Andrew Cooper; Xu, Dongxiao
> Cc: dario.faggioli@xxxxxxxxxx; Ian.Campbell@xxxxxxxxxx;
> Ian.Jackson@xxxxxxxxxxxxx; stefano.stabellini@xxxxxxxxxxxxx;
> xen-devel@xxxxxxxxxxxxx; konrad.wilk@xxxxxxxxxx; dgdegra@xxxxxxxxxxxxx;
> keir@xxxxxxx
> Subject: Re: [PATCH v6 4/7] x86: collect CQM information from all sockets
> 
> >>> On 28.01.14 at 15:34, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> > On 28/01/14 14:23, Xu, Dongxiao wrote:
> >>> And finally, I think the total size of the buffer here can easily
> >>> exceed a page, i.e. this then ends up being a non-order-0
> >>> allocation, which may _never_ succeed (i.e. the operation is
> >>> then rendered useless). I guest it'd be better to e.g. vmap()
> >>> the MFNs underlying the guest buffer.
> >> Do you mean we check the size of the total size, and allocate MFNs one by
> > one, then vmap them?
> >
> > I still think this is barking mad as a method of getting this quantity
> > of data from Xen to the toolstack in a repeated fashon.
> >
> > Xen should allocate a per-socket buffer at the start of day (or perhaps
> > on first use of CQM), and the CQM monitoring tool gets to map those
> > per-socket buffers read-only.
> >
> > This way, all processing of the CQM data happens in dom0 userspace, not
> > in Xen in hypercall context; All Xen has to do is periodically dump the
> > MSRs into the pages.
> 
> Indeed - if the nature of the data is such that it can be exposed
> read-only to suitably privileged entities, then this would be the
> much better interface.

If the data fetching is not hypercall driven, do you have a recommendation on 
how frequent Xen dumps the MSRs into the share page?

Thanks,
Dongxiao 

> 
> Jan


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