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Date: Thu, 12 Oct 2017 13:35:08 +0100
From: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20171012123508.GE5957@stefanha-x1.localdomain>
References: <20170929033844.26935-1-peterx@redhat.com>
	<20170929033844.26935-11-peterx@redhat.com>
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Subject: Re: [Qemu-devel] [RFC v2 10/22] monitor: allow to use IO thread for
 parsing
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To: Peter Xu <peterx@redhat.com>
Cc: qemu-devel@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>, "Daniel P . Berrange" <berrange@redhat.com>, Stefan Hajnoczi <shajnocz@redhat.com>, Fam Zheng <famz@redhat.com>, Juan Quintela <quintela@redhat.com>, mdroth@linux.vnet.ibm.com, Eric Blake <eblake@redhat.com>, Laurent Vivier <lvivier@redhat.com>, =?iso-8859-1?Q?Marc-Andr=E9?= Lureau <marcandre.lureau@gmail.com>, Markus Armbruster <armbru@redhat.com>, "Dr . David Alan Gilbert" <dgilbert@redhat.com>

On Fri, Sep 29, 2017 at 11:38:32AM +0800, Peter Xu wrote:
> For each Monitor, add one field "use_io_thr" to show whether it will be
> using the dedicated monitor IO thread to handle input/output.  When set,
> monitor IO parsing work will be offloaded to dedicated monitor IO
> thread, rather than the original main loop thread.

Why make use_io_thr optional?  We'd have to maintain and test both code
paths.

> @@ -4135,19 +4139,37 @@ void monitor_init(Chardev *chr, int flags)
>          monitor_read_command(mon, 0);
>      }
>  
> +    if (mon->use_io_thr) {
> +        /*
> +         * When use_io_thr is set, we use the global shared dedicated
> +         * IO thread for this monitor to handle input/output.
> +         */
> +        context = monitor_io_context_get();
> +        /* We should have inited globals before reaching here. */
> +        assert(context);
> +    } else {
> +        /* The default main loop, which is the main thread */
> +        context = NULL;
> +    }
> +
> +    /*
> +     * Hang the monitor before running it (which is triggered by

s/Hang/Add/

"Hang" isn't used as a verb for adding items to collections.  People
would probably think about deadlocking the thread instead :-).

> +     * qemu_chr_fe_set_handlers).  Otherwise one monitor may run while
> +     * find itself not on the mon_list.
> +     */
> +    qemu_mutex_lock(&monitor_lock);
> +    QTAILQ_INSERT_HEAD(&mon_list, mon, entry);
> +    qemu_mutex_unlock(&monitor_lock);