From: Peter Maydell <peter.maydell@linaro.org>
To: "Philippe Mathieu-Daudé" <philmd@redhat.com>
Cc: Richard Henderson <richard.henderson@linaro.org>,
QEMU Developers <qemu-devel@nongnu.org>,
Niek Linnenbank <nieklinnenbank@gmail.com>,
qemu-arm <qemu-arm@nongnu.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Igor Mammedov <imammedo@redhat.com>
Subject: Re: Sudden slowdown of ARM emulation in master
Date: Wed, 26 Feb 2020 08:48:26 +0000 [thread overview]
Message-ID: <CAFEAcA-32ddJW0ULWzGDDwLcvPGnXOatRHy73Agh0NRajfnRCQ@mail.gmail.com> (raw)
In-Reply-To: <ffa87cab-e85c-c381-289a-fdf1ef07b45a@redhat.com>
On Wed, 26 Feb 2020 at 08:44, Philippe Mathieu-Daudé <philmd@redhat.com> wrote:
>
> On 2/26/20 9:41 AM, Peter Maydell wrote:
> > On Tue, 25 Feb 2020 at 23:08, Niek Linnenbank <nieklinnenbank@gmail.com> wrote:
> >
> >> Just now I was working on some small fixes for the cubieboard machine and rebasing my Allwinner H3 branches.
> >> While doing some testing, I noticed that suddenly the machines were much slower than before.
> >> I only see this happening when I rebase to this commit:
> >> ca6155c0f2bd39b4b4162533be401c98bd960820 ("Merge tag 'patchew/20200219160953.13771-1-imammedo@redhat.com' of https://github.com/patchew-project/qemu into HEAD")
> >
> > Yeah, I noticed a slowdown yesterday as well, but haven't tracked it down
> > as yet. The first thing would be to do a git bisect to try to narrow
> > down what commit caused it.
>
> My guess: biggest chunk of memory is the DRAM, registered as "fast RAM"
> by QEMU, but the SoCs provide SRAM which is supposed to be faster. Not
> anymore with QEMU. And Linux try to use the SRAM when possible.
Doesn't sound very likely to me: generally Linux doesn't use random small
lumps of SRAM, it just goes for whatever the dtb says is the main RAM,
usually DRAM. And I thought that all RAM blocks within QEMU performed
the same?
From the commit that Howard tracked down as the cause it looks like
an ordering-of-actions issue in vl.c where something that was assuming
memory-size-related stuff was set up is now running before those
variables/fields are set correctly rather than after ?
thanks
-- PMM
next prev parent reply other threads:[~2020-02-26 8:55 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-25 23:07 Sudden slowdown of ARM emulation in master Niek Linnenbank
2020-02-26 8:41 ` Peter Maydell
2020-02-26 8:44 ` Philippe Mathieu-Daudé
2020-02-26 8:48 ` Peter Maydell [this message]
2020-02-26 8:51 ` Philippe Mathieu-Daudé
2020-02-26 8:45 ` Howard Spoelstra
2020-02-26 9:11 ` Igor Mammedov
2020-02-26 9:19 ` Igor Mammedov
2020-02-26 9:32 ` Howard Spoelstra
2020-02-26 10:14 ` Igor Mammedov
2020-02-26 10:03 ` Peter Maydell
2020-02-26 10:36 ` Mark Cave-Ayland
2020-02-26 14:13 ` Alex Bennée
2020-02-26 14:45 ` Igor Mammedov
2020-02-26 15:29 ` Alex Bennée
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