From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1NFRvP-0007jk-O0 for qemu-devel@nongnu.org; Tue, 01 Dec 2009 07:33:47 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1NFRvL-0007jA-83 for qemu-devel@nongnu.org; Tue, 01 Dec 2009 07:33:47 -0500 Received: from [199.232.76.173] (port=41834 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NFRvL-0007j7-3W for qemu-devel@nongnu.org; Tue, 01 Dec 2009 07:33:43 -0500 Received: from goliath.siemens.de ([192.35.17.28]:17904) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1NFRvK-0003bj-QO for qemu-devel@nongnu.org; Tue, 01 Dec 2009 07:33:43 -0500 Message-ID: <4B150D22.5070801@siemens.com> Date: Tue, 01 Dec 2009 13:33:38 +0100 From: Jan Kiszka MIME-Version: 1.0 Subject: Re: [Qemu-devel] Re: [PATCH 0/7] KVM SMP support, early version References: <1259256300-23937-1-git-send-email-glommer@redhat.com> <4B12B042.9020409@web.de> <5d6222a80911300342x4d29653as6c23acac598dec64@mail.gmail.com> <5d6222a80911300755o4fed5447w9ddae1abaccf7100@mail.gmail.com> <4B13F570.4030605@redhat.com> <5d6222a80911300847w2faa9d39nb2fc6ee3ccb9ccfd@mail.gmail.com> <4B140141.1040708@siemens.com> <4B1507AA.5050502@redhat.com> <4B15096A.5060801@siemens.com> <5d6222a80912010420q6ef5b433mcc75855b2b3d7968@mail.gmail.com> In-Reply-To: <5d6222a80912010420q6ef5b433mcc75855b2b3d7968@mail.gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Glauber Costa Cc: Glauber Costa , "aliguori@us.ibm.com" , Avi Kivity , "qemu-devel@nongnu.org" Glauber Costa wrote: > On Tue, Dec 1, 2009 at 10:17 AM, Jan Kiszka wrote: >> Avi Kivity wrote: >>> On 11/30/2009 07:30 PM, Jan Kiszka wrote: >>>>>> No. But what's wrong with on_vcpu? >>>>>> >>>>> intrinsically racy. signal passing slow down things, etc. >>>>> >>>>> That said, as I've stated many times: I don't believe there's anything >>>>> fundamentally wrong with on_vcpu. But we might get benefits from a re-design >>>>> of things to avoid it whenever possible. (just like the vcpu_reset() >>>>> I've just posted) >>>>> >>>>> >>>> If you don't want immediate execution of update_guest_debug, save the >>>> state that shall be transferred, set some flag, and run the transfer >>>> before guest entry inside the vcpu threads (after putting the registers >>>> as older kernels may otherwise overwrite the flags register). Should >>>> work, may even avoid redundant calls during a gdb session. >>>> >>> There's no guarantee the vcpu will ever exit to qemu, so you have to >>> signal the vcpu thread anyway. When you do that, you might as well load >>> the new state. >> Debugging is special here as it involves vmstop before you start playing >> with the debug settings. But I may also oversee some corner case right now. >> > > I imagined so. In this case, it might be better to set a flag before > vmstop, and then > honor it on vcpu entry. I had this feeling that in most cases where we > current signal the > vcpu, the VM will be already stopped anyway, so we don't need to resignal. > Do not set the flag before the machine stop, otherwise you risk to race with vcpus that exit and re-enter briefly before that. This manipulation should really be done under vmstop protection. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux