linux-kernel - Re: Feedback on 4.9 performance after PTI fixes

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Date:   Mon, 08 Jan 2018 18:07:54 +0100
From:   Yves-Alexis Perez <corsac@...ian.org>
To:     Willy Tarreau <w@....eu>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: Feedback on 4.9 performance after PTI fixes

On Sun, 2018-01-07 at 11:18 +0100, Willy Tarreau wrote:
>   - the highest performance impact on VMs comes from having PTI on the
>     guest kernel (-45%). At this point it makes no difference whether
>     the host kernel has it or not.

Hi Willy,

out of curiosity, is the pcid/invpcid flags exposed to and used by your guest
CPU? It might very well that the PCID optimisations are not used by the guests
here, and it might be worth either checking on bare metal or with the PCID
optimisations enabled.

Regards,
-- 
Yves-Alexis
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