Re: [Xen-devel] [PATCH v6 16/18] vmx: Add some scheduler hooks for VT-d posted interrupts

["Wu, Feng" <feng.wu@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Thursday, September 10, 2015 5:26 PM
> To: Wu, Feng
> Cc: Andrew Cooper; Dario Faggioli; George Dunlap; Tian, Kevin;
> xen-devel@xxxxxxxxxxxxx; Keir Fraser
> Subject: RE: [PATCH v6 16/18] vmx: Add some scheduler hooks for VT-d posted
> interrupts
> 
> >> > Anyway, I go through the main path of the code as below, I really don't 
> >> > find
> >> > anything unsafe here.
> >> >
> >> > context_switch() -->
> >> >     pi_ctxt_switch_from() -->
> >> >         vmx_pre_ctx_switch_pi() -->
> >> >             vcpu_unblock() -->
> >> >                 vcpu_wake() -->
> >> >                     SCHED_OP(VCPU2OP(v), wake, v) -->
> >> >                         csched_vcpu_wake() -->
> >> >                             __runq_insert()
> >> >                             __runq_tickle()
> >> >
> >> > If you continue to think it is unsafe, pointing out the place will be
> >> > welcome!
> >>
> >> Once again - I didn't say it's unsafe (and hence can't point at a
> >> particular place). What bothers me is that vcpu_unblock() affects
> >> scheduler state, and altering scheduler state from inside the
> >> context switch path looks problematic at the first glance. I'd be
> >> happy if I was told there is no such problem, but be aware that
> >> this would have to include latent ones: Even if right now things
> >> are safe, having such feedback have the potential of becoming
> >> an actual problem with a later scheduler change is already an
> >> issue, as finding the problem is then likely going to be rather hard
> >> (and I suspect it's not going to be you to debug this).
> >
> > What I can say is that after investigation, I don't find anything bad
> > for this vcpu_unblock(), I tested it in my experiment. So that is why
> > I'd like to ask some ideas from scheduler expects.
> 
> Agreed - I'm also awaiting their input.

Hi Dario, & George, could you please gave your thoughts about this?
Your input is very important for us!

Thanks,
Feng

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