Re: [Xen-devel] [PATCH] Remove a set operation for VCPU_KICK_SOFTIRQ when post interrupt to vm.

["Hanweidong (Randy)" <hanweidong@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 2015年9月7日 22:46
> To: Liuqiming (John)
> Cc: Hanweidong (Randy); Zhangwei (FF); yang.z.zhang@xxxxxxxxx; xen-
> devel@xxxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] [PATCH] Remove a set operation for
> VCPU_KICK_SOFTIRQ when post interrupt to vm.
> 
> >>> On 07.09.15 at 16:24, <john.liuqiming@xxxxxxxxxx> wrote:
> > I believe this also has something to do with a windows guest boot
> hang
> > issue.
> >
> > It randomly occured, when boot a guest has windows 2008 os and pv-
> driver
> > installed.
> > The boot process hangs when wait xenstored replay event signal.
> >
> > It can be reproduced after hundreds reboot using the xen staging
> branch.
> > But after I changed this code the hang issue can not reproduce.
> 
> The change below (which I don't think was ever posted to xen-devel)
> does not make any sense, as it prohibits timely delivery of guest
> interrupts. If there is an issue, I think you'd need to start with
> clearly

This change won't prohibit timely delivery of guest interrupts, intead, it 
helps to deliver guest interrupt timely. Posted interrupt delivery doesn't kick 
cpu, so it should not set VCPU_KICK_SOFTIRQ bit, and doesn't care about if 
VCPU_KICK_SOFTIRQ is set or not. if VCPU_KICK_SOFTIRQ is set, next interrupt 
will not be delivered due to test_and_set_bit check. What's more, it also 
impacts vcpu_kick() to kick cpu (smp_send_event_check_cpu) when 
VCPU_KICK_SOFTIRQ is set.

Weidong


> describing the issue you see and what you think it is being caused by.
> 
> Jan
> 
> > On 2015/9/7 22:46, - wrote:
> >> From: liuqiming 00178499 <john.liuqiming@xxxxxxxxxx>
> >>
> >> This set operation doesn't make any sense, and it will block later
> >> interrupt injected into vm (by vcpu_kick or deliver_posted_intr),
> >> which will cause a performance issue on CPU supporting posted-
> interrupt.
> >>
> >> Signed-off-by: Qiming Liu <john.liuqiming@xxxxxxxxxx>
> >> Cc: Yang Zhang <yang.z.zhang@xxxxxxxxx>
> >> ---
> >>   xen/arch/x86/hvm/vmx/vmx.c | 2 +-
> >>   1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> >> index 2582cdd..9480b44 100644
> >> --- a/xen/arch/x86/hvm/vmx/vmx.c
> >> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> >> @@ -1681,7 +1681,7 @@ static void
> __vmx_deliver_posted_interrupt(struct vcpu
> > *v)
> >>       {
> >>           unsigned int cpu = v->processor;
> >>
> >> -        if ( !test_and_set_bit(VCPU_KICK_SOFTIRQ,
> &softirq_pending(cpu))
> >> +        if ( !test_bit(VCPU_KICK_SOFTIRQ, &softirq_pending(cpu))
> >>                && (cpu != smp_processor_id()) )
> >>               send_IPI_mask(cpumask_of(cpu), posted_intr_vector);
> >>       }
> >
> >
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxx
> > http://lists.xen.org/xen-devel
> 
> 

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