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Re: [PATCH v20210111 08/39] xl: fix description of migrate --debug

  • To: Ian Jackson <iwj@xxxxxxxxxxxxxx>, Olaf Hering <olaf@xxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Mon, 8 Feb 2021 16:39:01 +0000
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  • Cc: <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>
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On 08/02/2021 16:25, Ian Jackson wrote:
> Olaf Hering writes ("[PATCH v20210111 08/39] xl: fix description of migrate 
> --debug"):
>> xl migrate --debug used to track every pfn in every batch of pages.
>> But these times are gone. Adjust the help text to tell what --debug
>> is supposed to do today.
> ...
>> -Display huge (!) amount of debug information during the migration process.
>> +Verify transferred domU page data. All memory will be transferred one more
>> +time to the destination host while the domU is paused, and compared with
>> +the result of the inital transfer while the domU was still running.
> Andy, as our expert on migration, can you confirm whether this is
> accurate ?
> Docs (including usage message) so
> Release-Acked-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>

Yeah - I totally changed what --debug did in migration v2, and this is
stale.  The legacy behaviour was unhelpful on any non-trivial guest.

It is possibly worth noting that you typically do see changed data when
using --debug, because of how the front/back pairs work.  This was a bit
of a curveball during development.




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