Re: [Xen-devel] [PATCH v9 08/17] vmx: Suppress posting interrupts when 'SN' is set

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Wu, Feng
> Sent: Tuesday, November 24, 2015 3:47 PM
> 
> 
> > -----Original Message-----
> > From: Tian, Kevin
> > Sent: Tuesday, November 24, 2015 3:30 PM
> > To: Wu, Feng <feng.wu@xxxxxxxxx>; xen-devel@xxxxxxxxxxxxx
> > Cc: Keir Fraser <keir@xxxxxxx>; Jan Beulich <jbeulich@xxxxxxxx>; Andrew
> > Cooper <andrew.cooper3@xxxxxxxxxx>
> > Subject: RE: [PATCH v9 08/17] vmx: Suppress posting interrupts when 'SN' is
> > set
> >
> > > From: Wu, Feng
> > > Sent: Tuesday, November 03, 2015 4:43 PM
> > N' is set
> > >
> > > Currently, we don't support urgent interrupt, all interrupts
> > > are recognized as non-urgent interrupt, so we cannot send
> > > posted-interrupt when 'SN' is set.
> > >
> > > CC: Kevin Tian <kevin.tian@xxxxxxxxx>
> > > CC: Keir Fraser <keir@xxxxxxx>
> > > CC: Jan Beulich <jbeulich@xxxxxxxx>
> > > CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > > Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
> > > Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > > Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> >
> > Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>, with one small comment:
> >
> > > +        do {
> > > +            /*
> > > +             * Currently, we don't support urgent interrupt, all
> > > +             * interrupts are recognized as non-urgent interrupt,
> > > +             * so we cannot send posted-interrupt when 'SN' is set.
> > > +             * Besides that, if 'ON' is already set, we cannot set
> > > +             * posted-interrupts as well.
> > > +             */
> >
> > Is above comment accurate. "cannot set" is too strong for 'ON'
> > already set, right? Ideally there's no correctness issue if you
> > still deliver another posted-interrupt even when ON is already set.
> > To me it's more like an optimization then it's cleaner to say
> > "we can avoid"...
> 
> Here, we just emulate the hardware's behavior, in hardware p.o.v,
> if 'ON' is set, the notification event will not be delivered, so here
> I try to follow the hardware, is this reasonable for you?
> 

I understand it's hardware behavior, just thought whether the comment
is too strong. Could we rephrase it as "Besides that, if 'ON' is already
set, no need to set posted-interrupts as well, according to hardware
behavior"?

Thanks
Kevin

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