[Qemu-devel] Re: [PATCH 4/4] Try not to exceed max downtime on stage3

[Liran Schour]

Jan Kiszka <address@hidden> wrote on 12/01/2010 13:51:09:

> Liran Schour wrote:
> > Move to stage3 only when remaining work can be done below max downtime.
> > To make sure the process will converge we will try only
> MAX_DIRTY_ITERATIONS.
>
> OK, that explains now patch 2. But do we have such barrier for memory
> migration as well? I don't thinks so, and I don't think this hard-coded
> limit is the right approach. Such thing should be derived from the
> bandwidth the user can control during runtime.

So if I understand you correctly you say that the way to assure convergence
is by the user controlling the bandwidth during runtime. So we can remove
this MAX_DIRTY_ITERATIONS.

> >
> > Signed-off-by: Liran Schour <address@hidden>
> > ---
> >  block-migration.c |   67 ++++++++++++++++++++++++++++++++++
> +-----------------
> >  1 files changed, 45 insertions(+), 22 deletions(-)
> >
> > diff --git a/block-migration.c b/block-migration.c
> > index 90c84b1..9ae04c4 100644
> > --- a/block-migration.c
> > +++ b/block-migration.c
> > @@ -17,6 +17,7 @@
> >  #include "qemu-queue.h"
> >  #include "monitor.h"
> >  #include "block-migration.h"
> > +#include "migration.h"
> >  #include <assert.h>
> >
> >  #define BLOCK_SIZE (BDRV_SECTORS_PER_DIRTY_CHUNK << BDRV_SECTOR_BITS)
> > @@ -30,6 +31,7 @@
> >  #define BLOCKS_READ_CHANGE 100
> >  #define INITIAL_BLOCKS_READ 100
> >  #define MAX_DIRTY_ITERATIONS 100
> > +#define DISK_RATE (30 << 20) //30 MB/sec
>
> IMHO a bad idea (e.g. mine was 6 MB/s last time I tried). Measure it
> during runtime just like the mem-migration does.
How about measuring the performance of reading BLOCK_SIZE and then compute
the disk rate? I can compute the average time to read BLOCK_SIZE and then
estimate the remaining time to complete the work.

Thanks,
- Liran