From: Willy Tarreau <w@1wt.eu>
To: Yves-Alexis Perez <corsac@debian.org>
Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: Feedback on 4.9 performance after PTI fixes
Date: Mon, 8 Jan 2018 19:26:22 +0100 [thread overview]
Message-ID: <20180108182622.GM10913@1wt.eu> (raw)
In-Reply-To: <1515431274.3305.59.camel@debian.org>
Hi Yves-Alexis,
On Mon, Jan 08, 2018 at 06:07:54PM +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.
You're totally right, I discovered during my later developments that
indeed PCID is not exposed there. So we take the hit of a full TLB
flush twice per syscall.
Willy
next prev parent reply other threads:[~2018-01-08 18:26 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-07 10:18 Feedback on 4.9 performance after PTI fixes Willy Tarreau
2018-01-08 17:07 ` Yves-Alexis Perez
2018-01-08 17:21 ` Yves-Alexis Perez
2018-01-08 18:26 ` Willy Tarreau [this message]
2018-01-08 20:26 ` Yves-Alexis Perez
2018-01-08 20:39 ` Willy Tarreau
2018-01-08 22:45 ` Pavlos Parissis
2018-01-08 17:26 ` David Laight
2018-01-09 7:09 ` Willy Tarreau
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180108182622.GM10913@1wt.eu \
--to=w@1wt.eu \
--cc=corsac@debian.org \
--cc=linux-kernel@vger.kernel.org \
--cc=stable@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.