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Tue, 8 Sep 2020 09:35:44 +0000 (UTC) Subject: Re: [PATCH v5 09/10] x68: acpi: trigger SMI before sending hotplug Notify event to OSPM To: Igor Mammedov References: <20200907112348.530921-1-imammedo@redhat.com> <20200907112348.530921-10-imammedo@redhat.com> <20200908093933.1b33ab5b@redhat.com> From: Laszlo Ersek Message-ID: <83fc69bf-cf64-06f9-522f-e5b3adebd7b7@redhat.com> Date: Tue, 8 Sep 2020 11:35:43 +0200 MIME-Version: 1.0 In-Reply-To: <20200908093933.1b33ab5b@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 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=205.139.110.61; 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 01:08:25 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.1, 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_H3=0.001, RCVD_IN_MSPIKE_WL=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 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"). Thanks! Laszlo