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

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Message-ID: <fdaddeb70a924e499fe9ee64c61fd9ed@AcuMS.aculab.com>
Date:   Mon, 8 Jan 2018 17:26:06 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Willy Tarreau' <w@....eu>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: Feedback on 4.9 performance after PTI fixes

From: Willy Tarreau
> Sent: 07 January 2018 10:19
...
> The impact inside VMs is quite big but it's not where we usuall install
> processes sensitive to syscall performance. I could find an even higher
> impact on a packet generation program dropping from 2.5 Mpps to 600kpps
> in the VM after the fix, but it doesn't make much sense to do this in
> VMs so I don't really care.

Why not?
It will be related to the cost of sending (and probably receiving)
network traffic in a VM.
This is something that is done a lot.

Maybe not packet generation, but a UDP/IP benchmark inside a VM would
be sensible.
It may well be that moderate ethernet packet rates cause a massive
performance drop when the host kernel has PTI enabled.

	David