Re: [PATCH v3 0/3] genirq/vfio: Introduce update_irq_devid and optimize VFIO irq ops

[luoben]

å 2019/8/20 äå11:22, Alex Williamson åé:
> On Tue, 20 Aug 2019 12:03:50 +0800
> luoben <luoben@xxxxxxxxxxxxxxxxx> wrote:
>
> > å 2019/8/20 äå4:51, Alex Williamson åé:
> > > On Thu, 15 Aug 2019 21:02:58 +0800
> > > Ben Luo <luoben@xxxxxxxxxxxxxxxxx> wrote:
> > >   
> > > > Currently, VFIO takes a lot of free-then-request-irq actions whenever
> > > > a VM (with device passthru via VFIO) sets irq affinity or mask/unmask
> > > > irq. Those actions only change the cookie data of irqaction or even
> > > > change nothing. The free-then-request-irq not only adds more latency,
> > > > but also increases the risk of losing interrupt, which may lead to a
> > > > VM hung forever in waiting for IO completion
> > > What guest environment is generating this?  Typically I don't see that
> > > Windows or Linux guests bounce the interrupt configuration much.
> > > Thanks,
> > >
> > > Alex
> > By tracing centos5u8 on host, I found it keep masking and unmasking
> > interrupt like this:
> >
> > [1566032533709879] index:28 irte_hi:000000010004a601
> > irte_lo:adb54bc000b98001
> > [1566032533711242] index:28 irte_hi:0000000000000000
> > irte_lo:0000000000000000
> > [1566032533711258] index:28 irte_hi:000000000004a601
> > irte_lo:00003fff00ac002d
> > [1566032533711269] index:28 irte_hi:000000000004a601
> > irte_lo:00003fff00ac002d
> [snip]
> > "[1566032533720007]" is timestamp in Îs, so centos5u8 tiggers 30+ irte
> > modification within 10ms
> Ok, that matches my understanding that only very old guests behave in
> this manner.  It's a curious case to optimize as RHEL5 is in extended
> life-cycle support, with regular maintenance releases ending 2+ years
> ago.  Thanks,
>
> Alex

But repeatedly set interrupt affinity in a new version guest can also 
cause the problem.


Thanks,

ÂÂÂ Ben