> -----Original Message----- > From: Dario Faggioli [mailto:dario.faggi...@citrix.com] > Sent: Wednesday, November 11, 2015 12:59 AM > To: Wu, Feng <feng...@intel.com>; xen-devel@lists.xen.org > Cc: Tian, Kevin <kevin.t...@intel.com>; Keir Fraser <k...@xen.org>; George > Dunlap <george.dun...@eu.citrix.com>; Andrew Cooper > <andrew.coop...@citrix.com>; Jan Beulich <jbeul...@suse.com> > Subject: Re: [Xen-devel] [PATCH v9 15/17] vmx: VT-d posted-interrupt core > logic > handling > > On Tue, 2015-11-03 at 09:07 +0000, Wu, Feng wrote: > > BTW, In the previous discussion, we will do the PI state adjustment > > in vmx_do_resume, however, seems this is not a good place to do this, > > since this function gets called only if the scheduling occurs, no > > matter it switches to another vCPU or continue runs the current vCPU. > > If no scheduling happens during "VM->Xen->VM", vmx-do_resume() will > > not get called. > > > Mmm... When I first read this, it seemed to me to be a good thing, and > a reason for actually putting your logic in there (that would avoid > paying the price of going through it during every VMENTRY, which you > were yourself hesitant about)! > > So, maybe I'm missing/misremembering something. Just to be sure, can > you tell me... > > > So I put the PI state adjustment code in vmx_vmenter_helper(), if you > > have any other good suggestions, please let me know, thanks a lot! > > > ... what is the reason(s) why you need to do the update even if no > scheduling happened? > > Looking at the code again, I think one reason may be to cope with when > vcpu_block() is called, but then local_events_need_delivery() returns > true, as shown here below: > > void vcpu_block(void) > { > struct vcpu *v = current; > > set_bit(_VPF_blocked, &v->pause_flags); > > arch_vcpu_block(v); // nv <--- > pi_wakeup_vector > > /* Check for events /after/ blocking: avoids wakeup waiting race. */ > if ( local_events_need_delivery() ) // <=== TRUE > clear_bit(_VPF_blocked, &v->pause_flags); > // we want nv == > posted_intr_vector, > so we need > vmx_pi_state_change() > to run, even if we're > not scheduling > } > > Is this the case?
Yes, that is the case, after arch_vcpu_block() is called, we don't cancel it even if there are events to be delivered, so we need to check whether the NV is the right value, if it isn't, which means after after arch_vcpu_block(),local_events_need_delivery() check returns true, so we need to adjust the PI state before VM-Entry. As Jan mentioned before, we will check the value before actually update it atomically, so I think it is okay from performance point of view. Thanks, Feng _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
