From 0459ddfdb31e7d812b555a2530ecbacdf96961a6 Mon Sep 17 00:00:00 2001 From: Nicholas Piggin Date: Wed, 9 Aug 2017 22:41:21 +1000 Subject: [PATCH] powerpc: NMI IPI improve lock primitive When the NMI IPI lock is contended, spin at low SMT priority, using loads only, and with interrupts enabled (where possible). This improves behaviour under high contention (e.g., a system crash when a number of CPUs are trying to enter the debugger). Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman --- arch/powerpc/kernel/smp.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c index cf0e1245b8cc..8d3320562c70 100644 --- a/arch/powerpc/kernel/smp.c +++ b/arch/powerpc/kernel/smp.c @@ -351,7 +351,7 @@ static void nmi_ipi_lock_start(unsigned long *flags) hard_irq_disable(); while (atomic_cmpxchg(&__nmi_ipi_lock, 0, 1) == 1) { raw_local_irq_restore(*flags); - cpu_relax(); + spin_until_cond(atomic_read(&__nmi_ipi_lock) == 0); raw_local_irq_save(*flags); hard_irq_disable(); } @@ -360,7 +360,7 @@ static void nmi_ipi_lock_start(unsigned long *flags) static void nmi_ipi_lock(void) { while (atomic_cmpxchg(&__nmi_ipi_lock, 0, 1) == 1) - cpu_relax(); + spin_until_cond(atomic_read(&__nmi_ipi_lock) == 0); } static void nmi_ipi_unlock(void) @@ -475,7 +475,7 @@ int smp_send_nmi_ipi(int cpu, void (*fn)(struct pt_regs *), u64 delay_us) nmi_ipi_lock_start(&flags); while (nmi_ipi_busy_count) { nmi_ipi_unlock_end(&flags); - cpu_relax(); + spin_until_cond(nmi_ipi_busy_count == 0); nmi_ipi_lock_start(&flags); } -- 2.39.2