Re: [Qemu-devel] how to pass pcid to guest?

[Stefan Priebe - Profihost AG]

Am 08.01.2018 um 23:07 schrieb Eric Blake:
> On 01/08/2018 02:03 PM, Stefan Priebe - Profihost AG wrote:
>> Hello,
>>
>> for meltdown mitigation and performance it's important to have the pcid
>> flag passed down to the guest (f.e.
>> https://groups.google.com/forum/m/#!topic/mechanical-sympathy/L9mHTbeQLNU).
> 
> Indeed; you are still waiting on the qemu patch mentioned here:
> https://www.qemu.org/2018/01/04/spectre/
> 
> which is still undergoing the review process, but should be up (in the
> form of 2.11.1) "in the next few days".

OK thanks as the performance difference is significant:

no pcid:
# time for i in $(seq 1 1 50); do du -sx /; done
...
real    0m26.614s
user    0m17.548s
sys     0m9.056s


kvm started with +pcid:
# time for i in $(seq 1 1 50); do du -sx /; done
...
real    0m14.734s
user    0m7.755s
sys     0m6.973s

Greets,
Stefan