diff options
author | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2019-05-17 12:50:42 +0200 |
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committer | Heiko Carstens <heiko.carstens@de.ibm.com> | 2019-06-15 12:25:52 +0200 |
commit | 38f2c691a4b3e89d476f8e8350d1ca299974b89d (patch) | |
tree | 8b4ab76fd8281be6dfcf8d5edc48d5ee522a4710 /arch/s390/include | |
parent | 7928260539f3a13b5b23a3fa0a7c0e4f5255940b (diff) |
s390: improve wait logic of stop_machine
The stop_machine loop to advance the state machine and to wait for all
affected CPUs to check-in calls cpu_relax_yield in a tight loop until
the last missing CPUs acknowledged the state transition.
On a virtual system where not all logical CPUs are backed by real CPUs
all the time it can take a while for all CPUs to check-in. With the
current definition of cpu_relax_yield a diagnose 0x44 is done which
tells the hypervisor to schedule *some* other CPU. That can be any
CPU and not necessarily one of the CPUs that need to run in order to
advance the state machine. This can lead to a pretty bad diagnose 0x44
storm until the last missing CPU finally checked-in.
Replace the undirected cpu_relax_yield based on diagnose 0x44 with a
directed yield. Each CPU in the wait loop will pick up the next CPU
in the cpumask of stop_machine. The diagnose 0x9c is used to tell the
hypervisor to run this next CPU instead of the current one. If there
is only a limited number of real CPUs backing the virtual CPUs we
end up with the real CPUs passed around in a round-robin fashion.
[heiko.carstens@de.ibm.com]:
Use cpumask_next_wrap as suggested by Peter Zijlstra.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Diffstat (limited to 'arch/s390/include')
-rw-r--r-- | arch/s390/include/asm/processor.h | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h index b0fcbc37b637..445ce9ee4404 100644 --- a/arch/s390/include/asm/processor.h +++ b/arch/s390/include/asm/processor.h @@ -36,6 +36,7 @@ #ifndef __ASSEMBLY__ +#include <linux/cpumask.h> #include <linux/linkage.h> #include <linux/irqflags.h> #include <asm/cpu.h> @@ -225,7 +226,7 @@ static __no_kasan_or_inline unsigned short stap(void) * Give up the time slice of the virtual PU. */ #define cpu_relax_yield cpu_relax_yield -void cpu_relax_yield(void); +void cpu_relax_yield(const struct cpumask *cpumask); #define cpu_relax() barrier() |