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Re: [Qemu-devel] [PATCH 1/1] monitor: increase amount of data for monito
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH 1/1] monitor: increase amount of data for monitor to read |
Date: |
Tue, 2 May 2017 17:36:30 +0100 |
User-agent: |
Mutt/1.8.0 (2017-02-23) |
* Markus Armbruster (address@hidden) wrote:
> "Denis V. Lunev" <address@hidden> writes:
>
> > On 05/02/2017 05:43 PM, Markus Armbruster wrote:
> >> "Denis V. Lunev" <address@hidden> writes:
> >>
> >>> Right now QMP and HMP monitors read 1 byte at a time from the socket,
> >>> which
> >>> is very inefficient. With 100+ VMs on the host this easily reasults in
> >>> a lot of unnecessary system calls and CPU usage in the system.
> >>>
> >>> This patch changes the amount of data to read to 4096 bytes, which matches
> >>> buffer size on the channel level. Fortunately, monitor protocol is
> >>> synchronous right now thus we should not face side effects in reality.
> >> Can you explain briefly why this relies on "synchronous"? I've spent
> >> all of two seconds on the question myself...
> > Each command is processed in sequence as it appears in the
> > channel. The answer to the command is sent and only after that
> > next command is processed.
>
> Yes, that's how QMP works.
>
> > Theoretically tith asynchronous processing we can have some side
> > effects due to changed buffer size.
>
> What kind of side effects do you have in mind?
>
> It's quite possible that this obviously inefficient way to read had some
> deep reason back when it was created. Hmm, git-blame is our friend:
>
> commit c62313bbdc48f72e93fa8196f2fff96ba35e4e9d
> Author: Jan Kiszka <address@hidden>
> Date: Fri Dec 4 14:05:29 2009 +0100
>
> monitor: Accept input only byte-wise
>
> This allows to suspend command interpretation and execution
> synchronously, e.g. during migration.
>
> Signed-off-by: Jan Kiszka <address@hidden>
> Signed-off-by: Anthony Liguori <address@hidden>
I don't think I understand why that's a problem; if we read more bytes,
we're not going to interpret them and execute them until after the previous
command returns are we?
Dave
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- [Qemu-devel] [PATCH 1/1] monitor: increase amount of data for monitor to read, Denis V. Lunev, 2017/05/02
- Re: [Qemu-devel] [PATCH 1/1] monitor: increase amount of data for monitor to read, Markus Armbruster, 2017/05/02
- Re: [Qemu-devel] [PATCH 1/1] monitor: increase amount of data for monitor to read, Denis V. Lunev, 2017/05/02
- Re: [Qemu-devel] [PATCH 1/1] monitor: increase amount of data for monitor to read, Markus Armbruster, 2017/05/02
- Re: [Qemu-devel] [PATCH 1/1] monitor: increase amount of data for monitor to read,
Dr. David Alan Gilbert <=
- Re: [Qemu-devel] [PATCH 1/1] monitor: increase amount of data for monitor to read, Daniel P. Berrange, 2017/05/02
- Re: [Qemu-devel] [PATCH 1/1] monitor: increase amount of data for monitor to read, Dr. David Alan Gilbert, 2017/05/02
- Re: [Qemu-devel] [PATCH 1/1] monitor: increase amount of data for monitor to read, Denis V. Lunev, 2017/05/02
- Re: [Qemu-devel] [PATCH 1/1] monitor: increase amount of data for monitor to read, Markus Armbruster, 2017/05/03
- Re: [Qemu-devel] [PATCH 1/1] monitor: increase amount of data for monitor to read, Daniel P. Berrange, 2017/05/03
- Re: [Qemu-devel] [PATCH 1/1] monitor: increase amount of data for monitor to read, Marc-André Lureau, 2017/05/03
- Re: [Qemu-devel] [PATCH 1/1] monitor: increase amount of data for monitor to read, Denis V. Lunev, 2017/05/03
- Re: [Qemu-devel] [PATCH 1/1] monitor: increase amount of data for monitor to read, Denis V. Lunev, 2017/05/03
- Re: [Qemu-devel] [PATCH 1/1] monitor: increase amount of data for monitor to read, Markus Armbruster, 2017/05/10
- Re: [Qemu-devel] [PATCH 1/1] monitor: increase amount of data for monitor to read, Denis V. Lunev, 2017/05/10