linux-kernel - [PATCH v2 2/2] x86: vdso: use __pvclock_read

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Message-Id: <1465994811-55091-3-git-send-email-pbonzini@redhat.com>
Date:	Wed, 15 Jun 2016 14:46:51 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:	x86@...nel.org, Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...hat.com>,
	Minfei Huang <mnghuan@...il.com>
Subject: [PATCH v2 2/2] x86: vdso: use __pvclock_read_cycles

The new simplified __pvclock_read_cycles does the same computation
as vread_pvclock, except that (because it takes the pvclock_vcpu_time_info
pointer) it has to be moved inside the loop.  Since the loop is expected to
never roll, this makes no difference.

Cc: Andy Lutomirski <luto@...capital.net>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Minfei Huang <mnghuan@...il.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
	If acked I'd like to take this through the KVM tree.

 arch/x86/entry/vdso/vclock_gettime.c | 16 +++-------------
 1 file changed, 3 insertions(+), 13 deletions(-)

diff --git a/arch/x86/entry/vdso/vclock_gettime.c b/arch/x86/entry/vdso/vclock_gettime.c
index db1e3b4c3693..94d54d0defa7 100644
--- a/arch/x86/entry/vdso/vclock_gettime.c
+++ b/arch/x86/entry/vdso/vclock_gettime.c
@@ -96,9 +96,8 @@ static notrace cycle_t vread_pvclock(int *mode)
 {
 	const struct pvclock_vcpu_time_info *pvti = &get_pvti0()->pvti;
 	cycle_t ret;
-	u64 tsc, pvti_tsc;
-	u64 last, delta, pvti_system_time;
-	u32 version, pvti_tsc_to_system_mul, pvti_tsc_shift;
+	u64 last;
+	u32 version;
 
 	/*
 	 * Note: The kernel and hypervisor must guarantee that cpu ID
@@ -130,18 +129,9 @@ static notrace cycle_t vread_pvclock(int *mode)
 			return 0;
 		}
 
-		tsc = rdtsc_ordered();
-		pvti_tsc_to_system_mul = pvti->tsc_to_system_mul;
-		pvti_tsc_shift = pvti->tsc_shift;
-		pvti_system_time = pvti->system_time;
-		pvti_tsc = pvti->tsc_timestamp;
+		ret = __pvclock_read_cycles(pvti);
 	} while (pvclock_read_retry(pvti, version));
 
-	delta = tsc - pvti_tsc;
-	ret = pvti_system_time +
-		pvclock_scale_delta(delta, pvti_tsc_to_system_mul,
-				    pvti_tsc_shift);
-
 	/* refer to vread_tsc() comment for rationale */
 	last = gtod->cycle_last;
 
-- 
1.8.3.1