llc_shared_mask is not cleared even if cpu is offline or hot removed.
So when hot-plugging CPU, the mask has wrong value. The mask is used
by CSF schduler. 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 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 cache of Socket#2 is shared with CPU#30-59 and 90-104.
So the mask has wrong value.
This patch fixes above problem by clearing llc_shared_mask bit of
offlined cpu.
Signed-off-by: Yasuaki Ishimatsu <isimatu.yasu...@jp.fujitsu.com>
---
arch/x86/kernel/smpboot.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 5492798..893cd2b 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1279,6 +1279,7 @@ __init void prefill_possible_map(void)
static void remove_siblinginfo(int cpu)
{
int sibling;
+ int llc_shared;
struct cpuinfo_x86 *c = &cpu_data(cpu);
for_each_cpu(sibling, cpu_core_mask(cpu)) {
@@ -1290,9 +1291,12 @@ static void remove_siblinginfo(int cpu)
cpu_data(sibling).booted_cores--;
}
+ for_each_cpu(llc_shared, cpu_llc_shared_mask(cpu))
+ cpumask_clear_cpu(cpu, cpu_llc_shared_mask(llc_shared));
for_each_cpu(sibling, cpu_sibling_mask(cpu))
cpumask_clear_cpu(cpu, cpu_sibling_mask(sibling));
cpumask_clear(cpu_sibling_mask(cpu));
+ cpumask_clear(cpu_llc_shared_mask(cpu));
cpumask_clear(cpu_core_mask(cpu));
c->phys_proc_id = 0;
c->cpu_core_id = 0;
--
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