[PATCH v3] x86,cpu-hotplug: assign same CPU number to readded CPU

[PATCH v3] x86,cpu-hotplug: assign same CPU number to readded CPU

[Yasuaki Ishimatsu]

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 <isimatu.yasuaki@jp.fujitsu.com>
Suggested-by: Borislav Petkov <bp@alien8.de>
---
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);

Re: [PATCH v3] x86,cpu-hotplug: assign same CPU number to readded CPU

[Toshi Kani]

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 <isimatu.yasuaki@jp.fujitsu.com>
> Suggested-by: Borislav Petkov <bp@alien8.de>

> ---
> 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 <toshi.kani@hp.com>

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. 

Re: [PATCH v3] x86,cpu-hotplug: assign same CPU number to readded CPU

[Toshi Kani]

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 <isimatu.yasuaki@jp.fujitsu.com>
> Suggested-by: Borislav Petkov <bp@alien8.de>

> ---
> 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 <toshi.kani@hp.com>

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. 

Re: [PATCH v3] x86,cpu-hotplug: assign same CPU number to readded CPU

[Yasuaki Ishimatsu]

(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 <isimatu.yasuaki@jp.fujitsu.com>
>> Suggested-by: Borislav Petkov <bp@alien8.de>
>
>> ---
>> 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 <toshi.kani@hp.com>

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.
>
>