Without this fix, /proc/cpuinfo will display an incorrect amount
of CPU cores, after bringing them offline and online again, as
exemplified below:
$ cat /proc/cpuinfo | grep cores
cpu cores : 4
cpu cores : 8
cpu cores : 8
cpu cores : 20
cpu cores : 4
cpu cores : 3
cpu cores : 2
cpu cores : 2
This patch fixes this by always zeroing the booted_cores variable
upon turning off a logical CPU.
Signed-off-by: Samuel Neves <[email protected]>
---
arch/x86/kernel/smpboot.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 9eee25d07586..ff99e2b6fc54 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1437,6 +1437,7 @@ static void remove_siblinginfo(int cpu)
cpumask_clear(topology_sibling_cpumask(cpu));
cpumask_clear(topology_core_cpumask(cpu));
c->cpu_core_id = 0;
+ c->booted_cores = 0;
cpumask_clear_cpu(cpu, cpu_sibling_setup_mask);
recompute_smt_state();
}
--
2.14.3
At 02/22/2018 04:50 AM, Samuel Neves wrote:
> Without this fix, /proc/cpuinfo will display an incorrect amount
> of CPU cores, after bringing them offline and online again, as
> exemplified below:
>
> $ cat /proc/cpuinfo | grep cores
> cpu cores : 4
> cpu cores : 8
> cpu cores : 8
> cpu cores : 20
> cpu cores : 4
> cpu cores : 3
> cpu cores : 2
> cpu cores : 2
>
> This patch fixes this by always zeroing the booted_cores variable
> upon turning off a logical CPU.
>
> Signed-off-by: Samuel Neves <[email protected]>
Yes, tested it in Qemu with 15 hot-pluggable CPUs, like below
...
-smp 1,maxcpus=16,sockets=2,cores=4,threads=2
...
When a new CPU bringups a new core, for each core in package, Linux
increments the booted_cores for this new cpu in set_cpu_sibling_map().
Due to the uncleared booted_cores, this incorrect number of CPU cores
will be shown.
Tested-by: Dou Liyang <[email protected]>
> ---
> arch/x86/kernel/smpboot.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 9eee25d07586..ff99e2b6fc54 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -1437,6 +1437,7 @@ static void remove_siblinginfo(int cpu)
> cpumask_clear(topology_sibling_cpumask(cpu));
> cpumask_clear(topology_core_cpumask(cpu));
> c->cpu_core_id = 0;
> + c->booted_cores = 0;
> cpumask_clear_cpu(cpu, cpu_sibling_setup_mask);
> recompute_smt_state();
> }
>
Commit-ID: 4596749339e06dc7a424fc08a15eded850ed78b7
Gitweb: https://git.kernel.org/tip/4596749339e06dc7a424fc08a15eded850ed78b7
Author: Samuel Neves <[email protected]>
AuthorDate: Wed, 21 Feb 2018 20:50:36 +0000
Committer: Ingo Molnar <[email protected]>
CommitDate: Fri, 23 Feb 2018 08:47:47 +0100
x86/topology: Update the 'cpu cores' field in /proc/cpuinfo correctly across CPU hotplug operations
Without this fix, /proc/cpuinfo will display an incorrect amount
of CPU cores, after bringing them offline and online again, as
exemplified below:
$ cat /proc/cpuinfo | grep cores
cpu cores : 4
cpu cores : 8
cpu cores : 8
cpu cores : 20
cpu cores : 4
cpu cores : 3
cpu cores : 2
cpu cores : 2
This patch fixes this by always zeroing the booted_cores variable
upon turning off a logical CPU.
Tested-by: Dou Liyang <[email protected]>
Signed-off-by: Samuel Neves <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
---
arch/x86/kernel/smpboot.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 9eee25d07586..ff99e2b6fc54 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1437,6 +1437,7 @@ static void remove_siblinginfo(int cpu)
cpumask_clear(topology_sibling_cpumask(cpu));
cpumask_clear(topology_core_cpumask(cpu));
c->cpu_core_id = 0;
+ c->booted_cores = 0;
cpumask_clear_cpu(cpu, cpu_sibling_setup_mask);
recompute_smt_state();
}