From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-x243.google.com (mail-pg0-x243.google.com [IPv6:2607:f8b0:400e:c05::243]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3xS9rJ0LYRzDqvc for ; Wed, 9 Aug 2017 22:41:52 +1000 (AEST) Received: by mail-pg0-x243.google.com with SMTP id 83so5798831pgb.4 for ; Wed, 09 Aug 2017 05:41:51 -0700 (PDT) From: Nicholas Piggin To: linuxppc-dev@lists.ozlabs.org Cc: Nicholas Piggin , Paul Mackerras Subject: [PATCH 1/6] powerpc: NMI IPI improve lock primitive Date: Wed, 9 Aug 2017 22:41:21 +1000 Message-Id: <20170809124126.28907-2-npiggin@gmail.com> In-Reply-To: <20170809124126.28907-1-npiggin@gmail.com> References: <20170809124126.28907-1-npiggin@gmail.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 --- 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); } -- 2.13.3