linux-kernel - [tip:x86/urgent] x86/smpboot: Make optimization of delay calibration work correctly

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Message-ID: <tip-76ce7cfe35ef58f34e6ba85327afb5fbf6c3ff9b@git.kernel.org>
Date:   Tue, 7 Nov 2017 07:09:58 -0800
From:   tip-bot for Pavel Tatashin <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     mingo@...nel.org, hpa@...or.com, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, pasha.tatashin@...cle.com
Subject: [tip:x86/urgent] x86/smpboot: Make optimization of delay
 calibration work correctly

Commit-ID:  76ce7cfe35ef58f34e6ba85327afb5fbf6c3ff9b
Gitweb:     https://git.kernel.org/tip/76ce7cfe35ef58f34e6ba85327afb5fbf6c3ff9b
Author:     Pavel Tatashin <pasha.tatashin@...cle.com>
AuthorDate: Fri, 27 Oct 2017 20:11:00 -0400
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Tue, 7 Nov 2017 16:04:54 +0100

x86/smpboot: Make optimization of delay calibration work correctly

If the TSC has constant frequency then the delay calibration can be skipped
when it has been calibrated for a package already. This is checked in
calibrate_delay_is_known(), but that function is buggy in two aspects:

It returns 'false' if

  (!tsc_disabled && !cpu_has(&cpu_data(cpu), X86_FEATURE_CONSTANT_TSC)

which is obviously the reverse of the intended check and the check for the
sibling mask cannot work either because the topology links have not been
set up yet.

Correct the condition and move the call to set_cpu_sibling_map() before
invoking calibrate_delay() so the sibling check works correctly.

[ tglx: Rewrote changelong ]

Fixes: c25323c07345 ("x86/tsc: Use topology functions")
Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: peterz@...radead.org
Cc: bob.picco@...cle.com
Cc: steven.sistare@...cle.com
Cc: daniel.m.jordan@...cle.com
Cc: stable@...r.kernel.org
Link: https://lkml.kernel.org/r/20171028001100.26603-1-pasha.tatashin@oracle.com
---
 arch/x86/kernel/smpboot.c | 11 ++++++-----
 arch/x86/kernel/tsc.c     |  8 +++-----
 2 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index ad59edd..65a0ccd 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -194,6 +194,12 @@ static void smp_callin(void)
 	smp_store_cpu_info(cpuid);
 
 	/*
+	 * The topology information must be up to date before
+	 * calibrate_delay() and notify_cpu_starting().
+	 */
+	set_cpu_sibling_map(raw_smp_processor_id());
+
+	/*
 	 * Get our bogomips.
 	 * Update loops_per_jiffy in cpu_data. Previous call to
 	 * smp_store_cpu_info() stored a value that is close but not as
@@ -203,11 +209,6 @@ static void smp_callin(void)
 	cpu_data(cpuid).loops_per_jiffy = loops_per_jiffy;
 	pr_debug("Stack at about %p\n", &cpuid);
 
-	/*
-	 * This must be done before setting cpu_online_mask
-	 * or calling notify_cpu_starting.
-	 */
-	set_cpu_sibling_map(raw_smp_processor_id());
 	wmb();
 
 	notify_cpu_starting(cpuid);
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 796d96b..ad2b925 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1346,12 +1346,10 @@ void __init tsc_init(void)
 unsigned long calibrate_delay_is_known(void)
 {
 	int sibling, cpu = smp_processor_id();
-	struct cpumask *mask = topology_core_cpumask(cpu);
+	int constant_tsc = cpu_has(&cpu_data(cpu), X86_FEATURE_CONSTANT_TSC);
+	const struct cpumask *mask = topology_core_cpumask(cpu);
 
-	if (!tsc_disabled && !cpu_has(&cpu_data(cpu), X86_FEATURE_CONSTANT_TSC))
-		return 0;
-
-	if (!mask)
+	if (tsc_disabled || !constant_tsc || !mask)
 		return 0;
 
 	sibling = cpumask_any_but(mask, cpu);