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Re: [qemu-s390x] qemu-system-s390x slowdown (regression ?) with qemu v4.

From: Cornelia Huck
Subject: Re: [qemu-s390x] qemu-system-s390x slowdown (regression ?) with qemu v4.0.0
Date: Wed, 12 Jun 2019 22:37:09 +0200

On Wed, 12 Jun 2019 13:03:30 -0700
Guenter Roeck <address@hidden> wrote:

> Hi,
> I noticed that qemu-system-s390x is much slower when running qemu v4.0.0
> vs. qemu v3.1.0. Specifically, on a system with Ryzen 2700X, a boot test
> has a runtime of ~25 seconds with qemu v3.1.0, but ~67 seconds with qemu
> v4.0.0.  Mainline qemu as of today (6/12) is even worse, with a runtime
> of ~73 seconds.

This doesn't sound good...

> All of this is booting exactly the same kernel and root file system.
> All qemu versions are compiled locally with gcc 6.5.0, with the same
> configuration options enabled.

Can you share how you build your kernel (e.g. for which architecture
level) and how you start QEMU (do you specify any cpu model)?

> Is this a known problem ?

I'm not aware of any; cc:ing David and Richard in case they are aware
of something in s390x tcg that might slow things down.

> Thanks,
> Guenter

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