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

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Message-ID: <1515432097.3305.66.camel@debian.org>
Date:   Mon, 08 Jan 2018 18:21:37 +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 Mon, 2018-01-08 at 18:07 +0100, Yves-Alexis Perez wrote:
> 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.

More details on this: https://groups.google.com/forum/m/#!topic/mechanical-sympathy/L9mHTbeQLNU

Regards,
-- 
Yves-Alexis
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