From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1MOZb4-0004hm-Oo for qemu-devel@nongnu.org; Wed, 08 Jul 2009 12:02:14 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1MOZaz-0004fx-T5 for qemu-devel@nongnu.org; Wed, 08 Jul 2009 12:02:14 -0400 Received: from [199.232.76.173] (port=48175 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1MOZaz-0004fn-CM for qemu-devel@nongnu.org; Wed, 08 Jul 2009 12:02:09 -0400 Received: from e4.ny.us.ibm.com ([32.97.182.144]:54011) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1MOZay-0004cb-PH for qemu-devel@nongnu.org; Wed, 08 Jul 2009 12:02:08 -0400 Received: from d01relay04.pok.ibm.com (d01relay04.pok.ibm.com [9.56.227.236]) by e4.ny.us.ibm.com (8.13.1/8.13.1) with ESMTP id n68FufDq025115 for ; Wed, 8 Jul 2009 11:56:41 -0400 Received: from d01av03.pok.ibm.com (d01av03.pok.ibm.com [9.56.224.217]) by d01relay04.pok.ibm.com (8.13.8/8.13.8/NCO v9.2) with ESMTP id n68G27LX189530 for ; Wed, 8 Jul 2009 12:02:07 -0400 Received: from d01av03.pok.ibm.com (loopback [127.0.0.1]) by d01av03.pok.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id n68G27vV000414 for ; Wed, 8 Jul 2009 12:02:07 -0400 Message-ID: <4A54C2FC.1000109@us.ibm.com> Date: Wed, 08 Jul 2009 11:02:04 -0500 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH][RESEND] Add monitor command for system_reboot References: <20090707192631.GQ11590@us.ibm.com> <20090708075601.GJ28046@redhat.com> <4A549990.2060205@us.ibm.com> <20090708132623.GN26640@redhat.com> <4A54A367.3010603@us.ibm.com> <20090708135607.GO26640@redhat.com> <20090708154349.GT11590@us.ibm.com> <4A54C012.2080003@us.ibm.com> <20090708155810.GU11590@us.ibm.com> In-Reply-To: <20090708155810.GU11590@us.ibm.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Ryan Harper Cc: qemu-devel@nongnu.org, Gleb Natapov Ryan Harper wrote: >> It's a different class of non-determinism though. With >> system_powerdown, you make a request to the guest. You don't know >> whether the guest will comply with the request. The same level of >> non-determinism exists with ballooning. >> >> With system_reboot, you're taking an action (system_reset) and what's >> not deterministic is whether you're taking that action based on what >> someone requested on the monitor (system_reboot) verses whether you're >> taking that action based on something the user did (shutdown). In the >> later case, you're action is functionally incorrect. >> > > Only if the shutdown from the user occurs in timeout period. So, yes, > it's still present, but the window of the behavior can be much > smaller. > > I still think this is a reasonable approach even with that window. > It's still a policy decision and the question is whether QEMU is the right place to implement that policy. QEMU provides a mechanism today to implement this policy (system_powerdown followed by polling via info status followed by system_reset). I tend to agree with Avi that we don't want to implement these sort of policies in QEMU and that we instead want to take a PV approach that can let us eliminate the nastier non-determinism. -- Regards, Anthony Liguori