Re: [Lsf-pc] [LSF/MM TOPIC][LSF/MM ATTEND] NAPI polling for block drivers

Sagi Grimberg
2017-01-12T14:41:10Z

>> **Note: when I ran multiple threads on more cpus the performance
>> degradation phenomenon disappeared, but I tested on a VM with
>> qemu emulation backed by null_blk so I figured I had some other
>> bottleneck somewhere (that's why I asked for some more testing).
>
> That could be because of the vmexits as every MMIO access in the guest
> triggers a vmexit and if you poll with a low budget you do more MMIOs hence
> you have more vmexits.
>
> Did you do testing only in qemu or with real H/W as well?

I tried once. IIRC, I saw the same phenomenons...