Messages in this thread | | | Date | Tue, 20 Aug 2019 09:22:09 -0600 | From | Alex Williamson <> | Subject | Re: [PATCH v3 0/3] genirq/vfio: Introduce update_irq_devid and optimize VFIO irq ops |
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On Tue, 20 Aug 2019 12:03:50 +0800 luoben <luoben@linux.alibaba.com> wrote:
> 在 2019/8/20 上午4:51, Alex Williamson 写道: > > On Thu, 15 Aug 2019 21:02:58 +0800 > > Ben Luo <luoben@linux.alibaba.com> 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 μs, 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
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