Re: [Xen-devel] [PATCH 07/13] xen: generalized event channel operations

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Feb 05, 2013 at 05:23:21PM +0000, Wei Liu wrote:
> On Tue, 2013-02-05 at 17:19 +0000, Konrad Rzeszutek Wilk wrote:
> > On Tue, Feb 05, 2013 at 05:08:51PM +0000, Wei Liu wrote:
> > > On Tue, 2013-02-05 at 17:04 +0000, Konrad Rzeszutek Wilk wrote:
> > > > On Thu, Jan 31, 2013 at 02:47:01PM +0000, Wei Liu wrote:
> > > > > Use global pointers in common operations to allow for better code 
> > > > > sharing
> > > > > between N-level event channel.
> > > > >
> > > > > Functions which are not suitable for sharing are also taken care of.
> > > > >
> > > > > Also update drivers/xen/evtchn.c to use exported variable instead of 
> > > > > macro.
> > > > >
> > > > > Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> > > > > ---
> > > > >  drivers/xen/events.c |  180 
> > > > > ++++++++++++++++++++++++++++++++------------------
> > > > >  drivers/xen/evtchn.c |   12 ++--
> > > > >  include/xen/events.h |    2 +
> > > > >  3 files changed, 123 insertions(+), 71 deletions(-)
> > > > >
> > > > > diff --git a/drivers/xen/events.c b/drivers/xen/events.c
> > > > > index 0679d27..4820a52 100644
> > > > > --- a/drivers/xen/events.c
> > > > > +++ b/drivers/xen/events.c
> > > > > @@ -51,6 +51,16 @@
> > > > >  #include <xen/interface/hvm/hvm_op.h>
> > > > >  #include <xen/interface/hvm/params.h>
> > > > >
> > > > > +/* N-level event channel, starting from 2 */
> > > > > +unsigned int evtchn_level = 2;
> > > > 
> > > > What if the hypervisor does not support that? Shouldn't be by default
> > > > at 1?
> > > > 
> > > 
> > > the default implementation is 2 level. ;-)
> > 
> > I am looking at evtchn_pending and evtchn_mask in the 'struct
> > shared_info' (include/xen/interface/xen.h) and it is not obvious from
> > that. What am I missing? 
> > 
> 
> To avoid scanning the whole bitmap when doing upcall, every vcpu is
> equipped with a selector - embedded in struct vcpu_info.
> 
> So it is a 2-level event lookup path.
> 
Ah, OK. I was thinking of the normal 2 level lookup - like a page-table.

Could you include the explanation in the patch please? Thank you.

> 
> Wei
> 

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