linux-kernel - [patch 14/15] lib/vdso: Avoid highres update if clocksource is not VDSO capable

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Message-Id: <20200114185947.996078385@linutronix.de>
Date:   Tue, 14 Jan 2020 19:52:51 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, John Stultz <john.stultz@...aro.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Christophe Leroy <christophe.leroy@....fr>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paulburton@...nel.org>,
        James Hogan <jhogan@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Marc Zyngier <maz@...nel.org>
Subject: [patch 14/15] lib/vdso: Avoid highres update if clocksource is not VDSO capable

If the current clocksource is not VDSO capable there is no point in
updating the high resolution parts of the VDSO data.

Replace the architecture specific check with a check for a VDSO capable
clocksource and skip the update if there is none.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 arch/arm/include/asm/vdso/vsyscall.h |    7 -------
 include/asm-generic/vdso/vsyscall.h  |    7 -------
 kernel/time/vsyscall.c               |   14 +++++++-------
 3 files changed, 7 insertions(+), 21 deletions(-)

--- a/arch/arm/include/asm/vdso/vsyscall.h
+++ b/arch/arm/include/asm/vdso/vsyscall.h
@@ -22,13 +22,6 @@ struct vdso_data *__arm_get_k_vdso_data(
 #define __arch_get_k_vdso_data __arm_get_k_vdso_data
 
 static __always_inline
-bool __arm_update_vdso_data(void)
-{
-	return cntvct_ok;
-}
-#define __arch_update_vdso_data __arm_update_vdso_data
-
-static __always_inline
 void __arm_sync_vdso_data(struct vdso_data *vdata)
 {
 	flush_dcache_page(virt_to_page(vdata));
--- a/include/asm-generic/vdso/vsyscall.h
+++ b/include/asm-generic/vdso/vsyscall.h
@@ -11,13 +11,6 @@ static __always_inline struct vdso_data
 }
 #endif /* __arch_get_k_vdso_data */
 
-#ifndef __arch_update_vdso_data
-static __always_inline bool __arch_update_vdso_data(void)
-{
-	return true;
-}
-#endif /* __arch_update_vdso_data */
-
 #ifndef __arch_update_vsyscall
 static __always_inline void __arch_update_vsyscall(struct vdso_data *vdata,
 						   struct timekeeper *tk)
--- a/kernel/time/vsyscall.c
+++ b/kernel/time/vsyscall.c
@@ -71,15 +71,15 @@ void update_vsyscall(struct timekeeper *
 {
 	struct vdso_data *vdata = __arch_get_k_vdso_data();
 	struct vdso_timestamp *vdso_ts;
+	s32 clock_mode;
 	u64 nsec;
-	s32 mode;
 
 	/* copy vsyscall data */
 	vdso_write_begin(vdata);
 
-	mode = tk->tkr_mono.clock->vdso_clock_mode;
-	vdata[CS_HRES_COARSE].clock_mode	= mode;
-	vdata[CS_RAW].clock_mode		= mode;
+	clock_mode = tk->tkr_mono.clock->vdso_clock_mode;
+	vdata[CS_HRES_COARSE].clock_mode	= clock_mode;
+	vdata[CS_RAW].clock_mode		= clock_mode;
 
 	/* CLOCK_REALTIME also required for time() */
 	vdso_ts		= &vdata[CS_HRES_COARSE].basetime[CLOCK_REALTIME];
@@ -105,10 +105,10 @@ void update_vsyscall(struct timekeeper *
 	WRITE_ONCE(vdata[CS_HRES_COARSE].hrtimer_res, hrtimer_resolution);
 
 	/*
-	 * Architectures can opt out of updating the high resolution part
-	 * of the VDSO.
+	 * If the current clocksource is not VDSO capable, then spare the
+	 * update of the high reolution parts.
 	 */
-	if (__arch_update_vdso_data())
+	if (clock_mode != VDSO_CLOCKMODE_NONE)
 		update_vdso_data(vdata, tk);
 
 	__arch_update_vsyscall(vdata, tk);