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Tue, 8 Sep 2020 11:00:21 +0000 (UTC) Subject: Re: [PATCH v5 09/10] x68: acpi: trigger SMI before sending hotplug Notify event to OSPM From: Laszlo Ersek To: Igor Mammedov References: <20200907112348.530921-1-imammedo@redhat.com> <20200907112348.530921-10-imammedo@redhat.com> <20200908093933.1b33ab5b@redhat.com> <83fc69bf-cf64-06f9-522f-e5b3adebd7b7@redhat.com> Message-ID: Date: Tue, 8 Sep 2020 13:00:20 +0200 MIME-Version: 1.0 In-Reply-To: <83fc69bf-cf64-06f9-522f-e5b3adebd7b7@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=lersek@redhat.com X-Mimecast-Spam-Score: 0.002 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US Received-SPF: pass client-ip=207.211.31.81; envelope-from=lersek@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/08 03:00:34 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: boris.ostrovsky@oracle.com, qemu-devel@nongnu.org, aaron.young@oracle.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 09/08/20 11:35, Laszlo Ersek wrote: > On 09/08/20 09:39, Igor Mammedov wrote: >> On Mon, 7 Sep 2020 17:17:52 +0200 >> Laszlo Ersek wrote: > >>> 1 Method (CSCN, 0, Serialized) >>> 2 { >>> 3 Acquire (\_SB.PCI0.PRES.CPLK, 0xFFFF) >>> 4 Name (CNEW, Package (0xFF){}) >>> 5 Local_Uid = Zero >>> 6 Local_HasJob = One >>> 7 While ((Local_HasJob == One)) >>> 8 { >>> 9 Local_HasJob = Zero >>> 10 Local_HasEvent = One >>> 11 Local_NumAddedCpus = Zero >>> 12 While (((Local_HasEvent == One) && (Local_Uid < 0x08))) >>> 13 { >>> 14 Local_HasEvent = Zero >>> 15 \_SB.PCI0.PRES.CSEL = Local_Uid >>> 16 \_SB.PCI0.PRES.CCMD = Zero >>> 17 If ((\_SB.PCI0.PRES.CDAT < Local_Uid)) >>> 18 { >>> 19 Break >>> 20 } >>> 21 >>> 22 If ((Local_NumAddedCpus == 0xFF)) >>> 23 { >>> 24 Local_HasJob = One >>> 25 Break >>> 26 } >>> 27 >>> 28 Local_Uid = \_SB.PCI0.PRES.CDAT >>> 29 If ((\_SB.PCI0.PRES.CINS == One)) >>> 30 { >>> 31 CNEW [Local_NumAddedCpus] = Local_Uid >>> 32 Local_NumAddedCpus++ >>> 33 Local_HasEvent = One >>> 34 } >>> 35 ElseIf ((\_SB.PCI0.PRES.CRMV == One)) >>> 36 { >>> 37 CTFY (Local_Uid, 0x03) >>> 38 \_SB.PCI0.PRES.CRMV = One >>> 39 Local_HasEvent = One >>> 40 } >>> 41 >>> 42 Local_Uid++ >>> 43 } >>> 44 >>> 45 If ((Local_NumAddedCpus > Zero)) >>> 46 { >>> 47 \_SB.PCI0.SMI0.SMIC = 0x04 >>> 48 } >>> 49 >>> 50 Local_CpuIdx = Zero >>> 51 While ((Local_CpuIdx < Local_NumAddedCpus)) >>> 52 { >>> 53 Local_Uid = DerefOf (CNEW [Local_CpuIdx]) >>> 54 CTFY (Local_Uid, One) >>> 55 Debug = Local_Uid >>> 56 \_SB.PCI0.PRES.CSEL = Local_Uid >>> 57 \_SB.PCI0.PRES.CINS = One >>> 58 Local_CpuIdx++ >>> 59 } >>> 60 } >>> 61 >>> 62 Release (\_SB.PCI0.PRES.CPLK) >>> 63 } >>> >>> When we take the Break on line 25, then: >>> >>> (a) on line 25, the following equality holds: >>> >>> Local_Uid == CNEW[Local_NumAddedCpus - 1] + 1 >>> >>> (b) on line 60, the following equality holds: >>> >>> Local_Uid == CNEW[Local_NumAddedCpus - 1] >>> >>> This means that, when we write Local_Uid to CSEL on line 15 again, then: >>> >>> - we effectively re-investigate the last-cached CPU (with selector value >>> CNEW[Local_NumAddedCpus - 1]) >>> >>> - rather than resuming the scanning right after it -- that is, with >>> selector value (CNEW[Local_NumAddedCpus - 1] + 1) --, in the spirit of >>> line 42. >>> >>> My question is: is this "rewind" intentional? >>> >>> Now, I don't see a functionality problem with this, as on line 57, we >>> clear the pending insert event for the last-cached CPU, so when we >>> re-check it, the "get pending" command will simply seek past it. >>> >>> But I'd like to understand if this is *precisely* your intent, or if >>> it's an oversight and it just ends up working OK. >> it's the later (it should not have any adverse effects) so I didn't care >> much about restarting from the last processed CPU. >> >> how about moving >> >> 22 If ((Local_NumAddedCpus == 0xFF)) >> 23 { >> 24 Local_HasJob = One >> 25 Break >> 26 } >> >> right after >> 40 } >> 41 >> 42 Local_Uid++ >> >> instead of adding extra 'if' at the end of outer loop? > > That only seems to save a CSEL write on line 15, during the first > iteration of the outer loop. And we would still re-select the last > selector from CNEW, in the second iteration of the outer loop. > > But, again, there's no bug; I just wanted to understand your intent. > > Can you please squash the following patch: > >> diff --git a/hw/acpi/cpu.c b/hw/acpi/cpu.c >> index 12839720018e..8dd4d8ebbf55 100644 >> --- a/hw/acpi/cpu.c >> +++ b/hw/acpi/cpu.c >> @@ -601,6 +601,15 @@ void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts, >> aml_append(while_ctx, aml_increment(cpu_idx)); >> } >> aml_append(while_ctx2, while_ctx); >> + /* >> + * If another batch is needed, then it will resume scanning >> + * exactly at -- and not after -- the last CPU that's currently >> + * in CPU_ADDED_LIST. In other words, the last CPU in >> + * CPU_ADDED_LIST is going to be re-checked. That's OK: we've >> + * just cleared the insert event for *all* CPUs in >> + * CPU_ADDED_LIST, including the last one. So the scan will >> + * simply seek past it. >> + */ >> } >> aml_append(method, while_ctx2); >> aml_append(method, aml_release(ctrl_lock)); > > With that: > > Reviewed-by: Laszlo Ersek > > I'll also follow up with test results for this patch (meaning a lowered > "max_cpus_per_pass"). Tested-by: Laszlo Ersek