linux-kernel - [RFC PATCH 06/10] x86: smp: remove call to ipi_call_lock()/ipi_call

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Date:	Tue, 29 May 2012 15:16:01 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	ralf@...ux-mips.org, sshtylyov@...sta.com, david.daney@...ium.com,
	nikunj@...ux.vnet.ibm.com, paulmck@...ux.vnet.ibm.com,
	axboe@...nel.dk, mingo@...nel.org, tglx@...utronix.de,
	peterz@...radead.org, akpm@...ux-foundation.org,
	srivatsa.bhat@...ux.vnet.ibm.com, Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: [RFC PATCH 06/10] x86: smp: remove call to ipi_call_lock()/ipi_call_unlock()

From: Yong Zhang <yong.zhang@...driver.com>

1) call_function.lock used in smp_call_function_many() is just to protect
   call_function.queue and &data->refs, cpu_online_mask is outside of the
   lock. And it's not necessary to protect cpu_online_mask,
   because data->cpumask is pre-calculate and even if a cpu is brougt up
   when calling arch_send_call_function_ipi_mask(), it's harmless because
   validation test in generic_smp_call_function_interrupt() will take care
   of it.

2) For cpu down issue, stop_machine() will guarantee that no concurrent
   smp_call_fuction() is processing.

Signed-off-by: Yong Zhang <yong.zhang0@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: x86@...nel.org
Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc: Jeremy Fitzhardinge <jeremy@...p.org>
---
 arch/x86/kernel/smpboot.c |    9 ---------
 arch/x86/xen/smp.c        |    2 --
 2 files changed, 0 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 433529e..bfbe30e 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -253,22 +253,13 @@ notrace static void __cpuinit start_secondary(void *unused)
 	check_tsc_sync_target();
 
 	/*
-	 * We need to hold call_lock, so there is no inconsistency
-	 * between the time smp_call_function() determines number of
-	 * IPI recipients, and the time when the determination is made
-	 * for which cpus receive the IPI. Holding this
-	 * lock helps us to not include this cpu in a currently in progress
-	 * smp_call_function().
-	 *
 	 * We need to hold vector_lock so there the set of online cpus
 	 * does not change while we are assigning vectors to cpus.  Holding
 	 * this lock ensures we don't half assign or remove an irq from a cpu.
 	 */
-	ipi_call_lock();
 	lock_vector_lock();
 	set_cpu_online(smp_processor_id(), true);
 	unlock_vector_lock();
-	ipi_call_unlock();
 	per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE;
 	x86_platform.nmi_init();
 
diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index afb250d..f58dca7 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -80,9 +80,7 @@ static void __cpuinit cpu_bringup(void)
 
 	notify_cpu_starting(cpu);
 
-	ipi_call_lock();
 	set_cpu_online(cpu, true);
-	ipi_call_unlock();
 
 	this_cpu_write(cpu_state, CPU_ONLINE);
 
-- 
1.7.5.4

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