llc_shared_map is not cleared even if CPU is offline or hot removed.
So when hot-plugging CPU and assigning new CPU number to hot-added CPU,
the mask has wrong value. The mask is used by CSF schduler to create
sched_domain. So it breaks CFS scheduler.
Here is a example on my system.
My system has 4 sockets and each socket has 15 cores and HT is enabled.
In this case, each core of sockes is numbered as follows:
| CPU#
Socket#0 | 0-14 , 60-74
Socket#1 | 15-29, 75-89
Socket#2 | 30-44, 90-104
Socket#3 | 45-59, 105-119
Then llc_shared_mask of CPU#30 has 0x3fff80000001fffc0000000.
It means that last level cache of Socket#2 is shared with
CPU#30-44 and 90-104.
When hot-removing socket#2 and #3, each core of sockets is numbered
as follows:
| CPU#
Socket#0 | 0-14 , 60-74
Socket#1 | 15-29, 75-89
But llc_shared_mask is not cleared. So llc_shared_mask of CPU#30 remains
having 0x3fff80000001fffc0000000.
After that, when hot-adding socket#2 and #3, each core of sockets is
numbered as follows:
| CPU#
Socket#0 | 0-14 , 60-74
Socket#1 | 15-29, 75-89
Socket#2 | 30-59
Socket#3 | 90-119
Then llc_shared_mask of CPU#30 becomes 0x3fff8000fffffffc0000000.
It means that last level cache of Socket#2 is shared with CPU#30-59
and 90-104. So the mask has wrong value.
At first, I cleared hot-removed CPU number's bit from llc_shared_map
when hot removing CPU. But Borislav suggested that the problem will
disappear if readded CPU is assigned same CPU number. And llc_shared_map
must not be changed.
So the patch assigns same CPU number to readded CPU by linking CPU
number to APIC ID. And by the patch, the problem disappers.
Signed-off-by: Yasuaki Ishimatsu <[email protected]>
Suggested-by: Borislav Petkov <[email protected]>
---
v2: change cpuid to cpunum
v3: fix Borislav's email address of Suggested-by
fix typo (ACPI ID to APIC ID)
---
arch/x86/kernel/apic/apic.c | 33 ++++++++++++++++++++++++++++++++-
1 file changed, 32 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index ad28db7..5dc3e50 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -220,6 +220,23 @@ static void apic_pm_activate(void);
static unsigned long apic_phys;
/*
+ * Bind APIC ID to Logical CPU number
+ * Logical CPU number to APIC ID does not change by this array
+ * even if CPU is hotplugged. So don't clear the array even if
+ * CPU is hot-removed
+ */
+static int apicid_to_cpunum[MAX_LOCAL_APIC] = {
+ [0 ... MAX_LOCAL_APIC-1] = -1,
+};
+
+/*
+ * Represent Logical CPU number bound to APIC ID
+ * Don't clear a bit even if CPU is hot-removed
+ */
+static DECLARE_BITMAP(cpu_used_bits, CONFIG_NR_CPUS);
+static struct cpumask *const cpu_used_mask = to_cpumask(cpu_used_bits);
+
+/*
* Get the LAPIC version
*/
static inline int lapic_get_version(void)
@@ -2122,6 +2139,17 @@ void disconnect_bsp_APIC(int virt_wire_setup)
apic_write(APIC_LVT1, value);
}
+static int get_cpunum(int apicid)
+{
+ int cpu;
+
+ cpu = apicid_to_cpunum[apicid];
+ if (cpu < 0)
+ cpu = cpumask_next_zero(-1, cpu_used_mask);
+
+ return cpu;
+}
+
int generic_processor_info(int apicid, int version)
{
int cpu, max = nr_cpu_ids;
@@ -2199,7 +2227,9 @@ int generic_processor_info(int apicid, int version)
*/
cpu = 0;
} else
- cpu = cpumask_next_zero(-1, cpu_present_mask);
+ cpu = get_cpunum(apicid);
+
+ apicid_to_cpunum[apicid] = cpu;
/*
* Validate version
@@ -2228,6 +2258,7 @@ int generic_processor_info(int apicid, int version)
early_per_cpu(x86_cpu_to_logical_apicid, cpu) =
apic->x86_32_early_logical_apicid(cpu);
#endif
+ cpumask_set_cpu(cpu, cpu_used_mask);
set_cpu_possible(cpu, true);
set_cpu_present(cpu, true);
On Thu, 2014-07-17 at 16:32 +0900, Yasuaki Ishimatsu wrote:
> llc_shared_map is not cleared even if CPU is offline or hot removed.
> So when hot-plugging CPU and assigning new CPU number to hot-added CPU,
> the mask has wrong value. The mask is used by CSF schduler to create
> sched_domain. So it breaks CFS scheduler.
>
> Here is a example on my system.
> My system has 4 sockets and each socket has 15 cores and HT is enabled.
> In this case, each core of sockes is numbered as follows:
>
> | CPU#
> Socket#0 | 0-14 , 60-74
> Socket#1 | 15-29, 75-89
> Socket#2 | 30-44, 90-104
> Socket#3 | 45-59, 105-119
>
> Then llc_shared_mask of CPU#30 has 0x3fff80000001fffc0000000.
> It means that last level cache of Socket#2 is shared with
> CPU#30-44 and 90-104.
>
> When hot-removing socket#2 and #3, each core of sockets is numbered
> as follows:
>
> | CPU#
> Socket#0 | 0-14 , 60-74
> Socket#1 | 15-29, 75-89
>
> But llc_shared_mask is not cleared. So llc_shared_mask of CPU#30 remains
> having 0x3fff80000001fffc0000000.
>
> After that, when hot-adding socket#2 and #3, each core of sockets is
> numbered as follows:
>
> | CPU#
> Socket#0 | 0-14 , 60-74
> Socket#1 | 15-29, 75-89
> Socket#2 | 30-59
> Socket#3 | 90-119
>
> Then llc_shared_mask of CPU#30 becomes 0x3fff8000fffffffc0000000.
> It means that last level cache of Socket#2 is shared with CPU#30-59
> and 90-104. So the mask has wrong value.
>
> At first, I cleared hot-removed CPU number's bit from llc_shared_map
> when hot removing CPU. But Borislav suggested that the problem will
> disappear if readded CPU is assigned same CPU number. And llc_shared_map
> must not be changed.
>
> So the patch assigns same CPU number to readded CPU by linking CPU
> number to APIC ID. And by the patch, the problem disappers.
>
> Signed-off-by: Yasuaki Ishimatsu <[email protected]>
> Suggested-by: Borislav Petkov <[email protected]>
> ---
> v2: change cpuid to cpunum
> v3: fix Borislav's email address of Suggested-by
> fix typo (ACPI ID to APIC ID)
> ---
> arch/x86/kernel/apic/apic.c | 33 ++++++++++++++++++++++++++++++++-
> 1 file changed, 32 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index ad28db7..5dc3e50 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -220,6 +220,23 @@ static void apic_pm_activate(void);
> static unsigned long apic_phys;
>
> /*
> + * Bind APIC ID to Logical CPU number
> + * Logical CPU number to APIC ID does not change by this array
> + * even if CPU is hotplugged. So don't clear the array even if
> + * CPU is hot-removed
> + */
> +static int apicid_to_cpunum[MAX_LOCAL_APIC] = {
> + [0 ... MAX_LOCAL_APIC-1] = -1,
> +};
> +
> +/*
> + * Represent Logical CPU number bound to APIC ID
> + * Don't clear a bit even if CPU is hot-removed
> + */
> +static DECLARE_BITMAP(cpu_used_bits, CONFIG_NR_CPUS);
> +static struct cpumask *const cpu_used_mask = to_cpumask(cpu_used_bits);
I think the name of cpu_used_mask is confusing since the term "used"
sounds some state of CPU, which is not the case here. How about
cpu_number_mask? This is more specific and avoids such confusion.
Otherwise, the change looks good.
Reviewed-by: Toshi Kani <[email protected]>
Thanks,
-Toshi
> +
> +/*
> * Get the LAPIC version
> */
^^
ps. I had a problem in applying this patch since there was an extra
blank character at the begging of unchanged lines. But this might be an
issue in my mailer.
On Thu, 2014-07-17 at 16:32 +0900, Yasuaki Ishimatsu wrote:
> llc_shared_map is not cleared even if CPU is offline or hot removed.
> So when hot-plugging CPU and assigning new CPU number to hot-added CPU,
> the mask has wrong value. The mask is used by CSF schduler to create
> sched_domain. So it breaks CFS scheduler.
>
> Here is a example on my system.
> My system has 4 sockets and each socket has 15 cores and HT is enabled.
> In this case, each core of sockes is numbered as follows:
>
> | CPU#
> Socket#0 | 0-14 , 60-74
> Socket#1 | 15-29, 75-89
> Socket#2 | 30-44, 90-104
> Socket#3 | 45-59, 105-119
>
> Then llc_shared_mask of CPU#30 has 0x3fff80000001fffc0000000.
> It means that last level cache of Socket#2 is shared with
> CPU#30-44 and 90-104.
>
> When hot-removing socket#2 and #3, each core of sockets is numbered
> as follows:
>
> | CPU#
> Socket#0 | 0-14 , 60-74
> Socket#1 | 15-29, 75-89
>
> But llc_shared_mask is not cleared. So llc_shared_mask of CPU#30 remains
> having 0x3fff80000001fffc0000000.
>
> After that, when hot-adding socket#2 and #3, each core of sockets is
> numbered as follows:
>
> | CPU#
> Socket#0 | 0-14 , 60-74
> Socket#1 | 15-29, 75-89
> Socket#2 | 30-59
> Socket#3 | 90-119
>
> Then llc_shared_mask of CPU#30 becomes 0x3fff8000fffffffc0000000.
> It means that last level cache of Socket#2 is shared with CPU#30-59
> and 90-104. So the mask has wrong value.
>
> At first, I cleared hot-removed CPU number's bit from llc_shared_map
> when hot removing CPU. But Borislav suggested that the problem will
> disappear if readded CPU is assigned same CPU number. And llc_shared_map
> must not be changed.
>
> So the patch assigns same CPU number to readded CPU by linking CPU
> number to APIC ID. And by the patch, the problem disappers.
>
> Signed-off-by: Yasuaki Ishimatsu <[email protected]>
> Suggested-by: Borislav Petkov <[email protected]>
> ---
> v2: change cpuid to cpunum
> v3: fix Borislav's email address of Suggested-by
> fix typo (ACPI ID to APIC ID)
> ---
> arch/x86/kernel/apic/apic.c | 33 ++++++++++++++++++++++++++++++++-
> 1 file changed, 32 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index ad28db7..5dc3e50 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -220,6 +220,23 @@ static void apic_pm_activate(void);
> static unsigned long apic_phys;
>
> /*
> + * Bind APIC ID to Logical CPU number
> + * Logical CPU number to APIC ID does not change by this array
> + * even if CPU is hotplugged. So don't clear the array even if
> + * CPU is hot-removed
> + */
> +static int apicid_to_cpunum[MAX_LOCAL_APIC] = {
> + [0 ... MAX_LOCAL_APIC-1] = -1,
> +};
> +
> +/*
> + * Represent Logical CPU number bound to APIC ID
> + * Don't clear a bit even if CPU is hot-removed
> + */
> +static DECLARE_BITMAP(cpu_used_bits, CONFIG_NR_CPUS);
> +static struct cpumask *const cpu_used_mask = to_cpumask(cpu_used_bits);
I think the name of cpu_used_mask is confusing since the term "used"
sounds representing some state of CPU, which is not the case here.
How about cpu_number_mask? This would be more specific, and avoid such
confusion.
Otherwise, the change looks good to me.
Reviewed-by: Toshi Kani <[email protected]>
Thanks,
-Toshi
> +
> +/*
> * Get the LAPIC version
> */
^^
ps. I had a problem in applying this patch since there was an extra
blank character at the begging of unchanged lines. But this might be an
issue in my mailer.
(2014/07/23 3:29), Toshi Kani wrote:
> On Thu, 2014-07-17 at 16:32 +0900, Yasuaki Ishimatsu wrote:
>> llc_shared_map is not cleared even if CPU is offline or hot removed.
>> So when hot-plugging CPU and assigning new CPU number to hot-added CPU,
>> the mask has wrong value. The mask is used by CSF schduler to create
>> sched_domain. So it breaks CFS scheduler.
>>
>> Here is a example on my system.
>> My system has 4 sockets and each socket has 15 cores and HT is enabled.
>> In this case, each core of sockes is numbered as follows:
>>
>> | CPU#
>> Socket#0 | 0-14 , 60-74
>> Socket#1 | 15-29, 75-89
>> Socket#2 | 30-44, 90-104
>> Socket#3 | 45-59, 105-119
>>
>> Then llc_shared_mask of CPU#30 has 0x3fff80000001fffc0000000.
>> It means that last level cache of Socket#2 is shared with
>> CPU#30-44 and 90-104.
>>
>> When hot-removing socket#2 and #3, each core of sockets is numbered
>> as follows:
>>
>> | CPU#
>> Socket#0 | 0-14 , 60-74
>> Socket#1 | 15-29, 75-89
>>
>> But llc_shared_mask is not cleared. So llc_shared_mask of CPU#30 remains
>> having 0x3fff80000001fffc0000000.
>>
>> After that, when hot-adding socket#2 and #3, each core of sockets is
>> numbered as follows:
>>
>> | CPU#
>> Socket#0 | 0-14 , 60-74
>> Socket#1 | 15-29, 75-89
>> Socket#2 | 30-59
>> Socket#3 | 90-119
>>
>> Then llc_shared_mask of CPU#30 becomes 0x3fff8000fffffffc0000000.
>> It means that last level cache of Socket#2 is shared with CPU#30-59
>> and 90-104. So the mask has wrong value.
>>
>> At first, I cleared hot-removed CPU number's bit from llc_shared_map
>> when hot removing CPU. But Borislav suggested that the problem will
>> disappear if readded CPU is assigned same CPU number. And llc_shared_map
>> must not be changed.
>>
>> So the patch assigns same CPU number to readded CPU by linking CPU
>> number to APIC ID. And by the patch, the problem disappers.
>>
>> Signed-off-by: Yasuaki Ishimatsu <[email protected]>
>> Suggested-by: Borislav Petkov <[email protected]>
>
>> ---
>> v2: change cpuid to cpunum
>> v3: fix Borislav's email address of Suggested-by
>> fix typo (ACPI ID to APIC ID)
>> ---
>> arch/x86/kernel/apic/apic.c | 33 ++++++++++++++++++++++++++++++++-
>> 1 file changed, 32 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
>> index ad28db7..5dc3e50 100644
>> --- a/arch/x86/kernel/apic/apic.c
>> +++ b/arch/x86/kernel/apic/apic.c
>> @@ -220,6 +220,23 @@ static void apic_pm_activate(void);
>> static unsigned long apic_phys;
>>
>> /*
>> + * Bind APIC ID to Logical CPU number
>> + * Logical CPU number to APIC ID does not change by this array
>> + * even if CPU is hotplugged. So don't clear the array even if
>> + * CPU is hot-removed
>> + */
>> +static int apicid_to_cpunum[MAX_LOCAL_APIC] = {
>> + [0 ... MAX_LOCAL_APIC-1] = -1,
>> +};
>> +
>> +/*
>> + * Represent Logical CPU number bound to APIC ID
>> + * Don't clear a bit even if CPU is hot-removed
>> + */
>> +static DECLARE_BITMAP(cpu_used_bits, CONFIG_NR_CPUS);
>> +static struct cpumask *const cpu_used_mask = to_cpumask(cpu_used_bits);
>
> I think the name of cpu_used_mask is confusing since the term "used"
> sounds some state of CPU, which is not the case here. How about
> cpu_number_mask? This is more specific and avoids such confusion.
I'll update it soon.
>
> Otherwise, the change looks good.
>
> Reviewed-by: Toshi Kani <[email protected]>
Thank you for review.
Thanks,
Yasuaki Ishimatsu
>
> Thanks,
> -Toshi
>
>> +
>> +/*
>> * Get the LAPIC version
>> */
> ^^
> ps. I had a problem in applying this patch since there was an extra
> blank character at the begging of unchanged lines. But this might be an
> issue in my mailer.
>
>