From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([140.186.70.92]:34335)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <kwolf@redhat.com>) id 1QYb72-0003Pm-Ly
	for qemu-devel@nongnu.org; Mon, 20 Jun 2011 05:49:45 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <kwolf@redhat.com>) id 1QYb71-0004Kh-41
	for qemu-devel@nongnu.org; Mon, 20 Jun 2011 05:49:44 -0400
Received: from mx1.redhat.com ([209.132.183.28]:38702)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <kwolf@redhat.com>) id 1QYb70-0004Kc-IA
	for qemu-devel@nongnu.org; Mon, 20 Jun 2011 05:49:42 -0400
Message-ID: <4DFF1854.3070003@redhat.com>
Date: Mon, 20 Jun 2011 11:52:20 +0200
From: Kevin Wolf <kwolf@redhat.com>
MIME-Version: 1.0
References: <4DF9BD9C.1060307@cn.fujitsu.com> <4DF9DD77.5040401@redhat.com>
	<20110616124651.GD14583@redhat.com>
	<4DFAAF00.900@cn.fujitsu.com> <4DFF0E9D.90409@redhat.com>
	<4DFF1596.8020902@cn.fujitsu.com>
In-Reply-To: <4DFF1596.8020902@cn.fujitsu.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH] do not send packet to nic if the packet
 will be dropped by nic
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Wen Congyang <wency@cn.fujitsu.com>
Cc: qemu-devel <qemu-devel@nongnu.org>, Aurelien Jarno <aurelien@aurel32.net>, "Michael S. Tsirkin" <mst@redhat.com>

Am 20.06.2011 11:40, schrieb Wen Congyang:
> At 06/20/2011 05:10 PM, Kevin Wolf Write:
>> Am 17.06.2011 03:33, schrieb Wen Congyang:
>>> If !s->clock_enabled or !rtl8139_receiver_enabled(s), it means that
>>> the nic will drop all packets from host. So qemu will keep getting
>>> packets from host and wasting CPU on dropping packets. This seems
>>> worse than packets that should be dropped but aren't.
>>>
>>> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
>>
>> Which bug does this change fix? I'm still not convinced that we should
>> do it.
> 
> Maybe not a bug fix now. As Michael S. Tsirkin said, if rtl8139_can_receive()
> returns 1, qemu will keep getting packets from host and wasting CPU on
> dropping packets. We can save CPU by return 0.

Don't we waste memory instead then because we leave the packets queued
indefinitely?

Kevin