From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38085) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aUAaC-0000x7-Gy for qemu-devel@nongnu.org; Fri, 12 Feb 2016 05:04:17 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aUAa9-0002Fe-6p for qemu-devel@nongnu.org; Fri, 12 Feb 2016 05:04:12 -0500 Received: from mx1.redhat.com ([209.132.183.28]:56663) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aUAa8-0002FS-VM for qemu-devel@nongnu.org; Fri, 12 Feb 2016 05:04:09 -0500 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by mx1.redhat.com (Postfix) with ESMTPS id 8104BC0C2373 for ; Fri, 12 Feb 2016 10:04:08 +0000 (UTC) Date: Fri, 12 Feb 2016 11:04:05 +0100 From: Igor Mammedov Message-ID: <20160212110405.26054513@nial.brq.redhat.com> In-Reply-To: <20160211161134.GC6239@thinpad.lan.raisama.net> References: <1454586455-10202-1-git-send-email-imammedo@redhat.com> <1454586455-10202-6-git-send-email-imammedo@redhat.com> <20160205152831.GR26314@thinpad.lan.raisama.net> <20160205171441.4d5e8b12@nial.brq.redhat.com> <20160211161134.GC6239@thinpad.lan.raisama.net> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 6/9] pc: acpi: create MADT.lapic entries only for valid lapics List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eduardo Habkost Cc: pbonzini@redhat.com, qemu-devel@nongnu.org, mst@redhat.com On Thu, 11 Feb 2016 14:11:34 -0200 Eduardo Habkost wrote: > On Fri, Feb 05, 2016 at 05:14:41PM +0100, Igor Mammedov wrote: > > On Fri, 5 Feb 2016 13:28:31 -0200 > > Eduardo Habkost wrote: > > > > > On Thu, Feb 04, 2016 at 12:47:32PM +0100, Igor Mammedov wrote: > > > > do not assume that all lapics in range 0..apic_id_limit > > > > are valid and do not create lapic entries for not > > > > possible lapics in MADT. > > > > > > > > Signed-off-by: Igor Mammedov > > > > > > Reviewed-by: Eduardo Habkost > > > > > > But there's one minor suggestion below: > > > > > > > --- > > > > hw/i386/acpi-build.c | 21 ++++++++++++++------- > > > > 1 file changed, 14 insertions(+), 7 deletions(-) > > > > > > > > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c > > > > index df13c7d..9eeeffa 100644 > > > > --- a/hw/i386/acpi-build.c > > > > +++ b/hw/i386/acpi-build.c > > > > @@ -361,9 +361,11 @@ build_fadt(GArray *table_data, GArray *linker, AcpiPmInfo *pm, > > > > } > > > > > > > > static void > > > > -build_madt(GArray *table_data, GArray *linker, AcpiCpuInfo *cpu, > > > > - PcGuestInfo *guest_info) > > > > +build_madt(GArray *table_data, GArray *linker, > > > > + MachineState *machine, PcGuestInfo *guest_info) > > > > { > > > > + MachineClass *mc = MACHINE_GET_CLASS(machine); > > > > + GArray *apic_id_list = mc->possible_cpu_arch_ids(); > > > > int madt_start = table_data->len; > > > > > > > > AcpiMultipleApicTable *madt; > > > > @@ -376,18 +378,23 @@ build_madt(GArray *table_data, GArray *linker, AcpiCpuInfo *cpu, > > > > madt->local_apic_address = cpu_to_le32(APIC_DEFAULT_ADDRESS); > > > > madt->flags = cpu_to_le32(1); > > > > > > > > - for (i = 0; i < guest_info->apic_id_limit; i++) { > > > > + for (i = 0; i < apic_id_list->len; i++) { > > > > AcpiMadtProcessorApic *apic = acpi_data_push(table_data, sizeof *apic); > > > > + CPUArchId id = FETCH_CPU_ARCH_ID(apic_id_list, i); > > > > + int apic_id = id.arch_id; > > > > + > > > > apic->type = ACPI_APIC_PROCESSOR; > > > > apic->length = sizeof(*apic); > > > > - apic->processor_id = i; > > > > - apic->local_apic_id = i; > > > > - if (test_bit(i, cpu->found_cpus)) { > > > > + apic->processor_id = apic_id; > > > > + apic->local_apic_id = apic_id; > > > > + if (id.cpu != NULL) { > > > > > > This seems to be the only place where CPUArchId.cpu is being used > > > (see my previous suggestion about making possible_cpu_arch_ids() > > > return just an uint64_t list). > > > > > > Also, using the existing found_cpus bitmap is more efficient than > > > making multiple calls to qemu_get_cpu_by_arch_id(). I wouldn't > > > mind keeping the bitmap. > > found_cpus bitmap is not better than (id.cpu != NULL) check > > the cost of filling both is about the same. > > The cost doesn't look the same. Populating found_cpus should be > O(smp_cpus)[1], and is being done only once. Filling id.cpu in > pc_possible_cpu_arch_ids() is O(max_cpus*smp_cpus), and it is > called multiple times. I've refactored patch to make pc_possible_cpu_arch_ids() linear, pls see v2: https://www.mail-archive.com/qemu-devel@nongnu.org/msg351298.html > > [1] I just noticed it is actually O(size_of_qom_tree), but it > is still linear, and could be changed to O(smp_cpus). > > > The issue I have with bitmap is that it's harder to generalize > > CPU hotplug code with it, while with possible_cpu_arch_ids() > > returned array I have a list of CPUs to work with without any > > assumptions on position in bitmap or array. > > Also bitmap scales worse than a list of CPUs if ID space > > is sparse and if ID is quite big. > > Yes, I agree that a list is better depending on how the arch ID > space is used. > > > That's why I'm dropping bitmap and switching to a list of > > IDs which in worst case is upto max_cpus. > > I think the possible_cpu_arch_ids() interface looks good, maybe > we just need to optimize it. > > But I'm not sure if we need to optimize it now, or if we can live > with the inefficient code and optimize it later. I won't complain > if we do it later, if we warn about it in the commit message or > comments. >