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From: Juan Quintela <quintela@redhat.com>
In-Reply-To: <20170720114812.GH2101@work-vm> (David Alan Gilbert's message of
	"Thu, 20 Jul 2017 12:48:12 +0100")
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Reply-To: quintela@redhat.com
Date: Tue, 08 Aug 2017 17:58:55 +0200
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Subject: Re: [Qemu-devel] [PATCH v5 10/17] migration: Create ram_multifd_page
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To: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Peter Xu <peterx@redhat.com>, qemu-devel@nongnu.org, lvivier@redhat.com, berrange@redhat.com

"Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:
> * Peter Xu (peterx@redhat.com) wrote:
>> On Wed, Jul 19, 2017 at 08:02:39PM +0100, Dr. David Alan Gilbert wrote:
>> ... here can we just do this?
>> 
>> retry:
>>     // don't take any lock, only read each p->address
>>     for (i = 0; i < multifd_send_state->count; i++) {
>>         p = &multifd_send_state->params[i];
>>         if (!p->address) {
>>             // we found one IDLE send thread
>>             break;
>>         }
>>     }
>>     if (!p) {
>>         qemu_sem_wait(&multifd_send_state->sem);
>>         goto retry;
>>     }
>>     // we switch its state, IDLE -> ACTIVE
>>     atomic_set(&p->address, address);
>>     // tell the thread to start work
>>     qemu_sem_post(&p->sem);
>> 
>> Above didn't really use any lock at all (either the per thread lock,
>> or the global lock). Would it work?
>
> I think what's there can certainly be simplified;  but also note
> that the later patch gets rid of 'address' and turns it into a count.
> My suggest was to keep the 'done' and stop using 'address' as something
> special; i.e. never write address in the thread; but I think yours might
> work as well.

I substitute the test from address == 0 to page.num == 0.

Notice that this is temporal, just to check that I am doing the things
right.  we end sending the pages here.

Later, Juan.