linux-kernel - [RFC PATCH v2 09/12] x86/apic: Use non-atomic operations when possible

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Message-Id: <20190531063645.4697-10-namit@vmware.com>
Date:   Thu, 30 May 2019 23:36:42 -0700
From:   Nadav Amit <namit@...are.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...el.com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Nadav Amit <namit@...are.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: [RFC PATCH v2 09/12] x86/apic: Use non-atomic operations when possible

Using __clear_bit() and __cpumask_clear_cpu() is more efficient than
using their atomic counterparts. Use them when atomicity is not needed,
such as when manipulating bitmasks that are on the stack.

Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Nadav Amit <namit@...are.com>
---
 arch/x86/kernel/apic/apic_flat_64.c   | 4 ++--
 arch/x86/kernel/apic/x2apic_cluster.c | 2 +-
 arch/x86/kernel/smp.c                 | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/apic/apic_flat_64.c b/arch/x86/kernel/apic/apic_flat_64.c
index 0005c284a5c5..65072858f553 100644
--- a/arch/x86/kernel/apic/apic_flat_64.c
+++ b/arch/x86/kernel/apic/apic_flat_64.c
@@ -78,7 +78,7 @@ flat_send_IPI_mask_allbutself(const struct cpumask *cpumask, int vector)
 	int cpu = smp_processor_id();
 
 	if (cpu < BITS_PER_LONG)
-		clear_bit(cpu, &mask);
+		__clear_bit(cpu, &mask);
 
 	_flat_send_IPI_mask(mask, vector);
 }
@@ -92,7 +92,7 @@ static void flat_send_IPI_allbutself(int vector)
 			unsigned long mask = cpumask_bits(cpu_online_mask)[0];
 
 			if (cpu < BITS_PER_LONG)
-				clear_bit(cpu, &mask);
+				__clear_bit(cpu, &mask);
 
 			_flat_send_IPI_mask(mask, vector);
 		}
diff --git a/arch/x86/kernel/apic/x2apic_cluster.c b/arch/x86/kernel/apic/x2apic_cluster.c
index 7685444a106b..609e499387a1 100644
--- a/arch/x86/kernel/apic/x2apic_cluster.c
+++ b/arch/x86/kernel/apic/x2apic_cluster.c
@@ -50,7 +50,7 @@ __x2apic_send_IPI_mask(const struct cpumask *mask, int vector, int apic_dest)
 	cpumask_copy(tmpmsk, mask);
 	/* If IPI should not be sent to self, clear current CPU */
 	if (apic_dest != APIC_DEST_ALLINC)
-		cpumask_clear_cpu(smp_processor_id(), tmpmsk);
+		__cpumask_clear_cpu(smp_processor_id(), tmpmsk);
 
 	/* Collapse cpus in a cluster so a single IPI per cluster is sent */
 	for_each_cpu(cpu, tmpmsk) {
diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index 04adc8d60aed..acddd988602d 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -146,7 +146,7 @@ void native_send_call_func_ipi(const struct cpumask *mask)
 	}
 
 	cpumask_copy(allbutself, cpu_online_mask);
-	cpumask_clear_cpu(smp_processor_id(), allbutself);
+	__cpumask_clear_cpu(smp_processor_id(), allbutself);
 
 	if (cpumask_equal(mask, allbutself) &&
 	    cpumask_equal(cpu_online_mask, cpu_callout_mask))
-- 
2.20.1