From mboxrd@z Thu Jan  1 00:00:00 1970
From: Pekka Enberg <penberg@kernel.org>
Subject: Re: [PATCH v2 4/4] kvm tools: Fix virtio console hangs by removing
 IRQ injection for tx path
Date: Sun, 08 May 2011 20:05:29 +0300
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	 <1304860165-28810-5-git-send-email-asias.hejun@gmail.com>
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Cc: Cyrill Gorcunov <gorcunov@gmail.com>, Ingo Molnar <mingo@elte.hu>,
	Sasha Levin <levinsasha928@gmail.com>,
	Prasad Joshi <prasadjoshi124@gmail.com>, kvm@vger.kernel.org
To: Asias He <asias.hejun@gmail.com>
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On Sun, 2011-05-08 at 21:09 +0800, Asias He wrote:
> As virtio spec says:
> 
> """
>  Because this is high importance and low bandwidth, the current Linux
>  implementation polls for the buffer to be used, rather than waiting
>  for an interrupt, simplifying the implementation signicantly.
> """
> 
> drivers/char/virtio_console.c
>  send_buf() {
>  ...
> 	/* Tell Host to go! */
> 	virtqueue_kick(out_vq);
>  ...
>         while (!virtqueue_get_buf(out_vq, &len))
>                 cpu_relax();
>  ...
>  }
> 
> The console hangs can simply be reproduced by yes command which
> gives tremendous console IOs and IRQs.

Sasha, does this fix the hangs you were seeing? We should re-enable
virtio console unconditionally if this does - that increases test
coverage for virtio console.

			Pekka