From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41321) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cYAWi-0005Yg-E3 for qemu-devel@nongnu.org; Mon, 30 Jan 2017 06:53:41 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cYAWf-0000vD-AC for qemu-devel@nongnu.org; Mon, 30 Jan 2017 06:53:40 -0500 Date: Mon, 30 Jan 2017 12:53:26 +0100 From: Igor Mammedov Message-ID: <20170130125326.2e9f4cc7@Igors-MacBook-Pro.local> In-Reply-To: <20170126142635.GA8653@in.ibm.com> References: <1466145399-32209-1-git-send-email-david@gibson.dropbear.id.au> <1466145399-32209-16-git-send-email-david@gibson.dropbear.id.au> <20170126123258.2d34fe95@Igors-MacBook-Pro.local> <20170126142635.GA8653@in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PULL 15/18] spapr: CPU hot unplug support List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Bharata B Rao Cc: peter.maydell@linaro.org, qemu-devel@nongnu.org, aik@ozlabs.ru, mdroth@linux.vnet.ibm.com, agraf@suse.de, qemu-ppc@nongnu.org, David Gibson On Thu, 26 Jan 2017 19:56:35 +0530 Bharata B Rao wrote: > On Thu, Jan 26, 2017 at 12:32:58PM +0100, Igor Mammedov wrote: > > On Fri, 17 Jun 2016 16:36:36 +1000 > > David Gibson wrote: > > > > > From: Bharata B Rao > > > > > > Remove the CPU core device by removing the underlying CPU thread devices. > > > Hot removal of CPU for sPAPR guests is achieved by sending the hot unplug > > > notification to the guest. Release the vCPU object after CPU hot unplug so > > > that vCPU fd can be parked and reused. > > > > > > Signed-off-by: Bharata B Rao > > > Signed-off-by: David Gibson > > [...] > > > > > > Bharata, > > > > Here is some notes I've made while auditing spapr cpu hotplug code. > > > > spapr_core_release() should be spapr_core_unrealize() > > except of machine related > > spapr->cores[cc->core_id / smt] = NULL; > > which should go to spapr_core_unplug() > > There were some issues in calling cpu_remove_[sync] from unrealize > path. I know that x86 does that way. let me remember and get back on this. on the first glance it doesn't look like there should be issues with making it spapr_core_unrealize(), but since it's way out of scope numa rework I'd leave 'fixing' it upto you. > > > > > > +static void spapr_core_release(DeviceState *dev, void *opaque) > > > +{ > > > + sPAPRCPUCore *sc = SPAPR_CPU_CORE(OBJECT(dev)); > > > + const char *typename = object_class_get_name(sc->cpu_class); > > > + size_t size = object_type_get_instance_size(typename); > > > + sPAPRMachineState *spapr = SPAPR_MACHINE(qdev_get_machine()); > > > + sPAPRCPUCore *core = SPAPR_CPU_CORE(OBJECT(dev)); > > > + CPUCore *cc = CPU_CORE(dev); > > > + int smt = kvmppc_smt_threads(); > > > + int i; > > > + > > > + for (i = 0; i < cc->nr_threads; i++) { > > > + void *obj = sc->threads + i * size; > > > + DeviceState *dev = DEVICE(obj); > > > + CPUState *cs = CPU(dev); > > > + PowerPCCPU *cpu = POWERPC_CPU(cs); > > > + > > > + spapr_cpu_destroy(cpu); > > > + cpu_remove_sync(cs); > > > + object_unparent(obj); > > > + } > > > + > > > + spapr->cores[cc->core_id / smt] = NULL; > > > + > > > + g_free(core->threads); > > > + object_unparent(OBJECT(dev)); > > > +} > > > + > > > > spapr_core_[un]plug() functions belong to machine code and should > > be in hw/ppc/spapr.c > > That's how the series started, but eventually we consolidated all > core related routines in spapr_cpu_core.c Since spapr_core_[un]plug() manage spapr machine state and not internal core state, I'd like to move them close to other machine code (spapr.c) if you don't mind. > > > > > > +void spapr_core_unplug(HotplugHandler *hotplug_dev, DeviceState *dev, > > > + Error **errp) > > > +{ > > > + sPAPRCPUCore *core = SPAPR_CPU_CORE(OBJECT(dev)); > > > + PowerPCCPU *cpu = POWERPC_CPU(core->threads); > > > + int id = ppc_get_vcpu_dt_id(cpu); > > > + sPAPRDRConnector *drc = > > > + spapr_dr_connector_by_id(SPAPR_DR_CONNECTOR_TYPE_CPU, id); > > > + sPAPRDRConnectorClass *drck; > > > + Error *local_err = NULL; > > > + > > > + g_assert(drc); > > > + > > > + drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc); > > > + drck->detach(drc, dev, spapr_core_release, NULL, &local_err); > > > > Could you explain call flow during cpu unplug? > > In response to unplug request, spapr_core_unplug() gets called which > does a detach() on the associated DRC object. The detach() registers > a callback (spapr_core_release) and signals the guest about the unplug > request. > > When the guest is ready to let go of the CPU core, DRC subsystem ends up > calling the callback spapr_core_release. For each of the CPU thread objects > of the core, spapr_core_release will call cpu_remove_sync() and waits > for the CPU to be really removed. cpu_remove will result in CPU unrealize > function being called (ppc_cpu_unrealizefn) for each of the removed > CPU. > > After we are done waiting for all the threads' removal, the core object is > ready for removal. > > > > > My expectations were that unplug_request() handler asks for CPU removal > > and unplug() handler removes CPU. > > It's obviously messed up somehow. > > When we did CPU unplug, we didn't really implement ->unplug_request() for > sPAPR. It was added later when memory unplug came in. It ended up that spapr_core_unplug() is called from both ->unplug_request() and ->unplug(). Where ->unplug() is dead path that's never called. I'll send patches to fix hot-unlpug flow to conform to generic hotplug pattern ->unplug_request() -> register callback and callback ->unplug() -> release_core() > > Regards, > Bharata. > >