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Re: [Qemu-devel] [PATCH v2 5/6] e1000: Choose which set of props to migr


From: Jason Wang
Subject: Re: [Qemu-devel] [PATCH v2 5/6] e1000: Choose which set of props to migrate
Date: Thu, 29 Mar 2018 16:26:53 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0



On 2018年03月29日 16:08, Dr. David Alan Gilbert wrote:
* Jason Wang (address@hidden) wrote:

On 2018年03月29日 00:36, Dr. David Alan Gilbert (git) wrote:
From: "Dr. David Alan Gilbert" <address@hidden>

When we're using the subsection we migrate both
the 'props' and 'tso_props' data; when we're not using
the subsection (to migrate to 2.11 or old machine types) we've
got to choose what to migrate in the main structure.

If we're using the subsection migrate 'props' in the main structure.
If we're not using the subsection then migrate the last one
that changed, which gives behaviour similar to the old behaviour.


But only after migration. Why not simply switch back to the old behavior if
migrate_tso_props if false?
Because:
   1) We know it's a broken behaviour so it's better not to unfix it
   2) The fix doesn't change guest visible behaviour other than actually
      sending the right packets; so there's no reason to make the fix
      itself dependent on the machine type.
   3) Gating the fix itself on the flag is actually more complex and
      would need checking the flag in lots of places that are already
      pretty complex, rather than what this does which is just check it
      in one place at migration.

It looks to me it was just something like:

    struct e1000x_txd_props *props = tp->cptse && chkflag(TSO) ? &tp->tso_props : &tp->props;

Btw, did this patch work when:

migrate A to B
migrate B to C

But there's no tx during B?

Thanks


Dave
Thanks

--
Dr. David Alan Gilbert / address@hidden / Manchester, UK





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