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Re: [PATCH v2 06/12] accel/tcg: better handle memory constrained systems
From: |
Daniel P . Berrangé |
Subject: |
Re: [PATCH v2 06/12] accel/tcg: better handle memory constrained systems |
Date: |
Thu, 23 Jul 2020 10:00:27 +0100 |
User-agent: |
Mutt/1.14.5 (2020-06-23) |
On Wed, Jul 22, 2020 at 12:02:59PM -0700, Richard Henderson wrote:
> On 7/22/20 9:44 AM, Daniel P. Berrangé wrote:
> > OpenStack uses TCG in alot of their CI infrastructure for example
> > and runs multiple VMs. If there's 4 VMs, that's another 4 GB of
> > RAM usage just silently added on top of the explicit -m value.
> >
> > I wouldn't be surprised if this pushes CI into OOM, even without
> > containers or cgroups being involved, as they have plenty of other
> > services consuming RAM in the CI VMs.
>
> I would hope that CI would also supply a -tb_size to go along with that -m
> value. Because we really can't guess on their behalf.
I've never even seen mention of -tb_size argument before myself, nor
seen anyone else using it and libvirt doesn't set it, so I think
this is not a valid assumption.
> > The commit 600e17b261555c56a048781b8dd5ba3985650013 talks about this
> > minimizing codegen cache flushes, but doesn't mention the real world
> > performance impact of eliminating those flushes ?
>
> Somewhere on the mailing list was this info. It was so dreadfully slow it was
> *really* noticable. Timeouts everywhere.
>
> > Presumably this makes the guest OS boot faster, but what's the before
> > and after time ? And what's the time like for values in between the
> > original 32mb and the new 1 GB ?
>
> But it wasn't "the original 32MB".
> It was the original "ram_size / 4", until that broke due to argument parsing
> ordering.
Hmm, 600e17b261555c56a048781b8dd5ba3985650013 says it was 32 MB as the
default in its commit message, which seems to match the code doing
#define DEFAULT_CODE_GEN_BUFFER_SIZE_1 (32 * MiB)
> I don't know what CI usually uses, but I usually use at least -m 4G, sometimes
> more. What's the libvirt default?
There's no default memory size - its up to whomever/whatever creates the
VMs to choose how much RAM is given.
Regards,
Daniel
--
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- [PATCH v2 01/12] shippable: add one more qemu to registry url, (continued)
- [PATCH v2 01/12] shippable: add one more qemu to registry url, Alex Bennée, 2020/07/22
- [PATCH v2 02/12] semihosting: defer connect_chardevs a little more to use serialx, Alex Bennée, 2020/07/22
- [PATCH v2 04/12] util: add qemu_get_host_physmem utility function, Alex Bennée, 2020/07/22
- [PATCH v2 03/12] semihosting: don't send the trailing '\0', Alex Bennée, 2020/07/22
- [PATCH v2 06/12] accel/tcg: better handle memory constrained systems, Alex Bennée, 2020/07/22
- Re: [PATCH v2 06/12] accel/tcg: better handle memory constrained systems, Richard Henderson, 2020/07/22
- Re: [PATCH v2 06/12] accel/tcg: better handle memory constrained systems, Alex Bennée, 2020/07/22
- Re: [PATCH v2 06/12] accel/tcg: better handle memory constrained systems, Daniel P . Berrangé, 2020/07/22
- Re: [PATCH v2 06/12] accel/tcg: better handle memory constrained systems, Richard Henderson, 2020/07/22
- Re: [PATCH v2 06/12] accel/tcg: better handle memory constrained systems,
Daniel P . Berrangé <=
- Re: [PATCH v2 06/12] accel/tcg: better handle memory constrained systems, Alex Bennée, 2020/07/23
- Re: [PATCH v2 06/12] accel/tcg: better handle memory constrained systems, Daniel P . Berrangé, 2020/07/23
- Re: [PATCH v2 06/12] accel/tcg: better handle memory constrained systems, Alex Bennée, 2020/07/23
[PATCH v2 05/12] util/oslib-win32: add qemu_get_host_physmem implementation, Alex Bennée, 2020/07/22
Re: [PATCH v2 05/12] util/oslib-win32: add qemu_get_host_physmem implementation, Yonggang Luo, 2020/07/22