Re: [Xen-devel] [PATCH 3/3] tools: introduce parameter max_ranges.

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Wei Liu [mailto:wei.liu2@xxxxxxxxxx]
> Sent: 19 January 2016 14:37
> To: Paul Durrant
> Cc: Wei Liu; Yu Zhang; xen-devel@xxxxxxxxxxxxx; Kevin Tian; Keir (Xen.org);
> Stefano Stabellini; Andrew Cooper; zhiyuan.lv@xxxxxxxxx;
> jbeulich@xxxxxxxx
> Subject: Re: [Xen-devel] [PATCH 3/3] tools: introduce parameter
> max_ranges.
> 
> On Tue, Jan 19, 2016 at 01:54:42PM +0000, Paul Durrant wrote:
> > > -----Original Message-----
> > > From: Wei Liu [mailto:wei.liu2@xxxxxxxxxx]
> > > Sent: 19 January 2016 11:54
> > > To: Yu Zhang
> > > Cc: xen-devel@xxxxxxxxxxxxx; Kevin Tian; Keir (Xen.org); Stefano 
> > > Stabellini;
> > > Andrew Cooper; Paul Durrant; zhiyuan.lv@xxxxxxxxx; jbeulich@xxxxxxxx;
> > > Wei Liu
> > > Subject: Re: [Xen-devel] [PATCH 3/3] tools: introduce parameter
> > > max_ranges.
> > >
> > > On Tue, Jan 19, 2016 at 05:27:58PM +0800, Yu Zhang wrote:
> > > > A new parameter - max_ranges is added to set the upper limit of
> ranges
> > > > to be tracked inside one ioreq server rangeset.
> > > >
> > > > Ioreq server uses a group of rangesets to track the I/O or memory
> > > > resources to be emulated. The default value of this limit is set to
> > > > 256. Yet there are circumstances under which the limit should exceed
> > > > the default one. E.g. in XenGT, when tracking the per-process graphic
> > > > translation tables on intel broadwell platforms, the number of page
> > > > tables concerned will be several thousand(normally in this case, 8192
> > > > could be a big enough value). Users who set his item explicitly are
> > > > supposed to know the specific scenarios that necessitate this
> > > > configuration.
> > > >
> > > > Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
> > > > ---
> > > >  docs/man/xl.cfg.pod.5           | 17 +++++++++++++++++
> > > >  tools/libxl/libxl_dom.c         |  3 +++
> > > >  tools/libxl/libxl_types.idl     |  1 +
> > > >  tools/libxl/xl_cmdimpl.c        |  4 ++++
> > > >  xen/arch/x86/hvm/hvm.c          |  7 ++++++-
> > > >  xen/include/public/hvm/params.h |  5 ++++-
> > > >  6 files changed, 35 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
> > > > index 8899f75..562563d 100644
> > > > --- a/docs/man/xl.cfg.pod.5
> > > > +++ b/docs/man/xl.cfg.pod.5
> > > > @@ -962,6 +962,23 @@ FIFO-based event channel ABI support up to
> > > 131,071 event channels.
> > > >  Other guests are limited to 4095 (64-bit x86 and ARM) or 1023 (32-bit
> > > >  x86).
> > > >
> > > > +=item B<max_ranges=N>
> > > > +
> > >
> > > This name is too generic. I don't have better suggestion though.
> > >
> >
> > I think the increased limit for XenGT need only be applied to wp mem
> ranges so perhaps the parameter name could be
> 'max_wp_memory_ranges'?
> >
> 
> What does "WP" mean? "Write Protected"?
> 

Yes.

> Is this parameter closely related to IOREQ server? Should it contain
> "ioreq" somehow?
> 

It is closely related but ioreq server is an implementation detail so do we 
want to expose it as a tunable? The concept we need to capture is that the 
toolstack can tune the limit of the maximum number of pages in the VM that can 
be set such that writes are emulated (but reads are as for normal ram). Or I 
guess we could get very specific and call it something like 'max_gtt_shadows'?

> Wei.

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