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Commit 0459ddfd authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
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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: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 7310d5c8

arch/powerpc/kernel/smp.c

+3 −3
Original line number Diff line number Diff line
@@ -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);

	}