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Date: Thu, 14 Jun 2018 10:21:30 +0800
From: Peter Xu <peterx@redhat.com>
Message-ID: <20180614022130.GQ15344@xz-mi>
References: <20180613102642.23995-1-dgilbert@redhat.com>
	<20180613102642.23995-3-dgilbert@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 2/3] migration: Wake rate limiting for
 urgent requests
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To: "Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>
Cc: qemu-devel@nongnu.org, quintela@redhat.com, jdenemar@redhat.com

On Wed, Jun 13, 2018 at 11:26:41AM +0100, Dr. David Alan Gilbert (git) wrote:

[...]

> @@ -2932,10 +2943,24 @@ static void *migration_thread(void *opaque)
>  
>          migration_update_counters(s, current_time);
>  
> +        urgent = false;
>          if (qemu_file_rate_limit(s->to_dst_file)) {
> -            /* usleep expects microseconds */
> -            g_usleep((s->iteration_start_time + BUFFER_DELAY -
> -                      current_time) * 1000);
> +            /* Wait for a delay to do rate limiting OR
> +             * something urgent to post the semaphore.
> +             */
> +            int ms = s->iteration_start_time + BUFFER_DELAY - current_time;
> +            trace_migration_thread_ratelimit_pre(ms);
> +            if (qemu_sem_timedwait(&s->rate_limit_sem, ms) == 0) {
> +                /* We were worken by one or more urgent things but
> +                 * the timedwait will have consumed one of them.
> +                 * The service routine for the urgent wake will dec
> +                 * the semaphore itself for each item it consumes,
> +                 * so add this one we just eat back.
> +                 */
> +                qemu_sem_post(&s->rate_limit_sem);

Is it possible that we just avoid eating that in the next patch?  Then
we only provide a helper to "trigger an urgent request" but we only
consume the point here?

-- 
Peter Xu