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Re: [Qemu-devel] migration: adding migration to/from a file (v2)
From: |
Jamie Lokier |
Subject: |
Re: [Qemu-devel] migration: adding migration to/from a file (v2) |
Date: |
Thu, 19 Feb 2009 19:37:33 +0000 |
User-agent: |
Mutt/1.5.13 (2006-08-11) |
Anthony Liguori wrote:
> Uri Lublin wrote:
> >Anthony Liguori wrote:
> >>Uri Lublin wrote:
> >>>
> >>>Migration to file, uses migration-to-fd (supports live migration).
> >>>Migration from file, uses qemu-fopen directly.
> >>
> >>Eh? Haven't we already talked about why this doesn't work? Maybe
> >>there's a v3 that you meant to send?
> >>
> >
> >Actually I do have a v3 which uses posix-aio-compat.c
> >It's a much more complicated solution then just writing to a file though.
> >Also I am not sure if I need to use a signal or not as the migration
> >(to-fd) code is polling. And if I use signal should I use SIGUSR2 or a
> >different one and use a pipe similar to block-raw-posix.c ?
>
> How is the migration code polling? It will attempt to do writes until a
> write returns EAGAIN. At this point, it will wait for notification that
> the more writes are available.
> Remember, migration is a streaming
> protocol, not a random access, so it only makes sense to have one
> outstanding request at a time.
Fwow, often with streaming (in general) the highest performance comes
from having two or more outstanding requests at a time, so there are
no gaps between requests being processed at the OS and device level.
However, unless migrate-to-file uses O_DIRECT that will be hidden by
the OS's buffering.
Then the remaining overhead from AIOs (or fake AIOs using threads) is
lots context switching, one per write completed.
-- Jamie
- Re: [Qemu-devel] migration: adding migration to/from a file (v2), (continued)
- Re: [Qemu-devel] migration: adding migration to/from a file (v2), Anthony Liguori, 2009/02/19
- Re: [Qemu-devel] migration: adding migration to/from a file (v2), Uri Lublin, 2009/02/19
- Re: [Qemu-devel] migration: adding migration to/from a file (v2), Anthony Liguori, 2009/02/19
- Re: [Qemu-devel] migration: adding migration to/from a file (v2), Uri Lublin, 2009/02/19
- Re: [Qemu-devel] migration: adding migration to/from a file (v2), Anthony Liguori, 2009/02/19
- Re: [Qemu-devel] migration: adding migration to/from a file (v2), Jamie Lokier, 2009/02/19
- Re: [Qemu-devel] migration: adding migration to/from a file (v2), M. Warner Losh, 2009/02/19
- Re: [Qemu-devel] migration: adding migration to/from a file (v2), Anthony Liguori, 2009/02/19
- Re: [Qemu-devel] migration: adding migration to/from a file (v2), M. Warner Losh, 2009/02/19
- Re: [Qemu-devel] migration: adding migration to/from a file (v2), Uri Lublin, 2009/02/19
- Re: [Qemu-devel] migration: adding migration to/from a file (v2),
Jamie Lokier <=
- Re: [Qemu-devel] migration: adding migration to/from a file (v2), Anthony Liguori, 2009/02/19
- Re: [Qemu-devel] migration: adding migration to/from a file (v2), Jamie Lokier, 2009/02/19