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

From: Stefan Priebe - Profihost AG
Subject: Re: [Qemu-devel] how to pass pcid to guest?
Date: Tue, 9 Jan 2018 14:12:11 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0

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


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