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Re: [Qemu-devel] [RFC] dataplane: IOThreads and writing dataplane-capabl
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [RFC] dataplane: IOThreads and writing dataplane-capable code |
Date: |
Thu, 8 May 2014 14:44:35 +0100 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
* Stefan Hajnoczi (address@hidden) wrote:
<snip>
> How to synchronize with an IOThread
> -----------------------------------
> AioContext is not thread-safe so some rules must be followed when using file
> descriptors, event notifiers, timers, or BHs across threads:
>
> 1. AioContext functions can be called safely from file descriptor, event
> notifier, timer, or BH callbacks invoked by the AioContext. No locking is
> necessary.
>
> 2. Other threads wishing to access the AioContext must use
> aio_context_acquire()/aio_context_release() for mutual exclusion. Once the
> context is acquired no other thread can access it or run event loop iterations
> in this AioContext.
>
> aio_context_acquire()/aio_context_release() calls may be nested. This
> means you can call them if you're not sure whether #1 applies.
>
> Side note: the best way to schedule a function call across threads is to
> create
> a BH in the target AioContext beforehand and then call qemu_bh_schedule(). No
> acquire/release or locking is needed for the qemu_bh_schedule() call. But be
> sure to acquire the AioContext for aio_bh_new() if necessary.
How do these IOThreads pause during migration?
Are they paused by the 'qemu_mutex_lock_iothread' that the migration thread
calls?
Dave
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK