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Re: [Qemu-devel] [PATCH v5 17/45] Add wrappers and handlers for sending/
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH v5 17/45] Add wrappers and handlers for sending/receiving the postcopy-ram migration messages. |
Date: |
Mon, 30 Mar 2015 21:23:42 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 |
On 30/03/2015 19:46, Dr. David Alan Gilbert wrote:
>>> > > +PostcopyState postcopy_state_get(MigrationIncomingState *mis)
>>> > > +{
>>> > > + return atomic_fetch_add(&mis->postcopy_state, 0);
>>> > > +}
>>> > > +
>>> > > +/* Set the state and return the old state */
>>> > > +PostcopyState postcopy_state_set(MigrationIncomingState *mis,
>>> > > + PostcopyState new_state)
>>> > > +{
>>> > > + return atomic_xchg(&mis->postcopy_state, new_state);
>>> > > +}
>> >
>> > Which are the (multiple) threads are calling these functions?
> The main thread receiving the migration and the postcopy ram_listen_thread
> receiving the RAM pages.
> It's not actually racy between multiple threads updating it,
> it's sequenced so that the main thread initialises it and then
> hands over to the listen thread that takes it over from that point.
I would use atomic_mb_read/atomic_mb_set here.
Paolo