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Date: Sun, 2 Aug 2015 13:40:14 +0100
From: Marc Zyngier <marc.zyngier@....com>
To: Lukasz Anaczkowski <lukasz.anaczkowski@...el.com>
Cc: tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
x86@...nel.org, jason@...edaemon.net, rjw@...ysocki.net,
len.brown@...el.com, pavel@....cz, linux-pm@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
Yinghai Lu <yinghai@...nel.org>
Subject: Re: [PATCH] x86, acpi: Handle lapic/x2apic entries in MADT
On Thu, 30 Jul 2015 19:43:39 +0200
Lukasz Anaczkowski <lukasz.anaczkowski@...el.com> wrote:
> From the ACPI spec:
> "Logical processors with APIC ID values less than 0xFF
> (whether in XAPIC or X2APIC mode) must use the Processor LAPIC
> structure [...]. Logical processors with APIC ID values 0xFF and
> greater must use the Processor Local x2APIC structure."
>
> Because of above, BIOS is first enumerating cores with HT with
> LAPIC values (<0xFF) and then rest with X2APIC values (>=0xFF).
>
> With current kernel code, where enumeration is in order:
> BSP, X2APIC, LAPIC
> enumeration on machine with more than 255 CPUs (each core with 4 HT)
> first X2APIC IDs get low logical CPU IDs (1..x) and then LAPIC IDs
> get higher logical CPU IDs (50..y), as in example below:
>
> Core LCpu ApicId LCpu ApicId LCpu ApicId LCpu ApicId
> 0 0 0000 97 0001 145 0002 193 0003
> 1 50 0004 98 0005 146 0006 194 0007
> 2 51 0010 99 0011 147 0012 195 0013
> 3 52 0014 100 0015 148 0016 196 0017
> 4 53 0018 101 0019 149 001a 197 001b
> 5 54 001c 102 001d 150 001e 198 001f
> ...
> 62 95 00f8 143 00f9 191 00fa 239 00fb
> 63 37 00ff 96 00fc 144 00fd 192 00fe
> 64 1 0100 13 0101 25 0102 38 0103
> 65 2 0104 14 0105 26 0106 39 0107
> ...
>
> (Core - physical core, LCpu - logical CPU, ApicId - ID assigned
> by BIOS).
>
> This is wrong for the following reasons:
> () it's hard to predict how cores and threads will be enumerated
> () when it's hard to predict, s/w threads cannot be properly affinitized
> causing significant performance impact due to e.g. inproper cache
> sharing
> () enumeration is inconsistent with how threads are enumerated on
> other Intel Xeon processors
>
> To fix this, each LAPIC/X2APIC entry from MADT table needs to be
> handled at the same time when processing it, thus adding
> acpi_subtable_proc structure which stores
> () ACPI table id
> () handler that processes table
> () counter how many items has been processed
> and passing it to acpi_table_parse_entries().
>
> Also, order in which MADT LAPIC/X2APIC handlers are passed is
> reversed to achieve correct CPU enumeration.
>
> In scenario when someone boots kernel with options 'maxcpus=72 nox2apic',
> in result less cores may be booted, since some of the CPUs the kernel
> will try to use will have APIC ID >= 0xFF. In such case, one
> should not pass 'nox2apic'.
>
> Disclimer: code parsing MADT LAPIC/X2APIC has not been touched since 2009,
> when X2APIC support was initially added. I do not know why MADT parsing
> code was added in the reversed order in the first place.
> I guess it didn't matter at that time since nobody cared about cores
> with APIC IDs >= 0xFF, right?
>
> This patch is based on work of "Yinghai Lu <yinghai@...nel.org>"
> previously published at https://lkml.org/lkml/2013/1/21/563,
> thus putting Yinghai Lu as 'Signed-off-by', as well.
>
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> Signed-off-by: Lukasz Anaczkowski <lukasz.anaczkowski@...el.com>
> ---
> arch/x86/kernel/acpi/boot.c | 29 +++++++++++++-----
> drivers/acpi/numa.c | 28 ++++++++++++-----
> drivers/acpi/tables.c | 75 ++++++++++++++++++++++++++++-----------------
> drivers/irqchip/irq-gic.c | 15 ++++++---
> include/linux/acpi.h | 13 ++++++--
> 5 files changed, 111 insertions(+), 49 deletions(-)
>
Hi Lukasz,
[...]
> diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
> index 4dd8826..d004a32 100644
> --- a/drivers/irqchip/irq-gic.c
> +++ b/drivers/irqchip/irq-gic.c
> @@ -1091,12 +1091,16 @@ gic_v2_acpi_init(struct acpi_table_header *table)
> {
> void __iomem *cpu_base, *dist_base;
> int count;
> + struct acpi_subtable_proc gic_proc;
> +
> + memset(gic_proc, 0, sizeof(gic_proc));
You haven't ever tried compiling this, have you?
> + gic_proc.id = ACPI_MADT_TYPE_GENERIC_INTERRUPT;
> + gic_proc.handler = gic_acpi_parse_madt_cpu;
>
> /* Collect CPU base addresses */
> count = acpi_parse_entries(ACPI_SIG_MADT,
> sizeof(struct acpi_table_madt),
> - gic_acpi_parse_madt_cpu, table,
> - ACPI_MADT_TYPE_GENERIC_INTERRUPT, 0);
> + table, gic_proc, 0);
This doesn't match the prototype below.
> if (count <= 0) {
> pr_err("No valid GICC entries exist\n");
> return -EINVAL;
> @@ -1106,10 +1110,13 @@ gic_v2_acpi_init(struct acpi_table_header *table)
> * Find distributor base address. We expect one distributor entry since
> * ACPI 5.1 spec neither support multi-GIC instances nor GIC cascade.
> */
> + memset(gic_proc, 0, sizeof(gic_proc));
> + gic_proc.id = ACPI_MADT_TYPE_GENERIC_DISTRIBUTOR;
> + gic_proc.handler = gic_acpi_parse_madt_distributor;
> +
> count = acpi_parse_entries(ACPI_SIG_MADT,
> sizeof(struct acpi_table_madt),
> - gic_acpi_parse_madt_distributor, table,
> - ACPI_MADT_TYPE_GENERIC_DISTRIBUTOR, 0);
> + table, gic_proc, 0);
> if (count <= 0) {
> pr_err("No valid GICD entries exist\n");
> return -EINVAL;
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index d2445fa..59b17e8 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -135,6 +135,12 @@ static inline void acpi_initrd_override(void *data, size_t size)
> (!entry) || (unsigned long)entry + sizeof(*entry) > end || \
> ((struct acpi_subtable_header *)entry)->length < sizeof(*entry))
>
> +struct acpi_subtable_proc {
> + int id;
> + acpi_tbl_entry_handler handler;
> + int count;
> +};
> +
> char * __acpi_map_table (unsigned long phys_addr, unsigned long size);
> void __acpi_unmap_table(char *map, unsigned long size);
> int early_acpi_boot_init(void);
> @@ -145,10 +151,13 @@ int acpi_numa_init (void);
>
> int acpi_table_init (void);
> int acpi_table_parse(char *id, acpi_tbl_table_handler handler);
> +int acpi_table_parse_entries_array(char *id, unsigned long table_size,
> + struct acpi_subtable_proc *proc, int proc_num,
> + unsigned int max_entries);
> int __init acpi_parse_entries(char *id, unsigned long table_size,
> - acpi_tbl_entry_handler handler,
> struct acpi_table_header *table_header,
> - int entry_id, unsigned int max_entries);
> + struct acpi_subtable_proc *proc, int proc_num,
Could you please check that it actually compiles when you enable ACPI
on arm64?
Thanks,
M.
--
Jazz is not dead. It just smells funny.
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