Subject: [PATCH V2 02/19] vdso: Consolidate nanoseconds calculation

From: Adrian Hunter <[email-masked]>
Date: Mon, 25 Mar 2024 08:40:06 +0200

Consolidate nanoseconds calculation to simplify and reduce code
duplication.

Suggested-by: Thomas Gleixner <[email-masked]>
Signed-off-by: Adrian Hunter <[email-masked]>
---

Changes in V2:
	Adjusted due to changes in "vdso: Consolidate vdso_calc_delta()"

 arch/x86/include/asm/vdso/gettimeofday.h | 17 +++++----
 lib/vdso/gettimeofday.c                  | 45 +++++++++++-------------
 2 files changed, 28 insertions(+), 34 deletions(-)

diff --git a/arch/x86/include/asm/vdso/gettimeofday.h b/arch/x86/include/asm/vdso/gettimeofday.h
index 8e048ca980df..5727dedd3549 100644
--- a/arch/x86/include/asm/vdso/gettimeofday.h
+++ b/arch/x86/include/asm/vdso/gettimeofday.h
@@ -300,7 +300,7 @@ static inline bool arch_vdso_cycles_ok(u64 cycles)
 #define vdso_cycles_ok arch_vdso_cycles_ok
 
 /*
- * x86 specific delta calculation.
+ * x86 specific calculation of nanoseconds for the current cycle count
  *
  * The regular implementation assumes that clocksource reads are globally
  * monotonic. The TSC can be slightly off across sockets which can cause
@@ -308,8 +308,8 @@ static inline bool arch_vdso_cycles_ok(u64 cycles)
  * jump.
  *
  * Therefore it needs to be verified that @cycles are greater than
- * @last. If not then use @last, which is the base time of the current
- * conversion period.
+ * @vd->cycles_last. If not then use @vd->cycles_last, which is the base
+ * time of the current conversion period.
  *
  * This variant also uses a custom mask because while the clocksource mask of
  * all the VDSO capable clocksources on x86 is U64_MAX, the above code uses
@@ -317,25 +317,24 @@ static inline bool arch_vdso_cycles_ok(u64 cycles)
  * declares everything with the MSB/Sign-bit set as invalid. Therefore the
  * effective mask is S64_MAX.
  */
-static __always_inline
-u64 vdso_calc_delta(u64 cycles, u64 last, u64 mask, u32 mult)
+static __always_inline u64 vdso_calc_ns(const struct vdso_data *vd, u64 cycles, u64 base)
 {
 	/*
 	 * Due to the MSB/Sign-bit being used as invalid marker (see
 	 * arch_vdso_cycles_valid() above), the effective mask is S64_MAX.
 	 */
-	u64 delta = (cycles - last) & S64_MAX;
+	u64 delta = (cycles - vd->cycle_last) & S64_MAX;
 
 	/*
 	 * Due to the above mentioned TSC wobbles, filter out negative motion.
 	 * Per the above masking, the effective sign bit is now bit 62.
 	 */
 	if (unlikely(delta & (1ULL << 62)))
-		return 0;
+		return base >> vd->shift;
 
-	return delta * mult;
+	return ((delta * vd->mult) + base) >> vd->shift;
 }
-#define vdso_calc_delta vdso_calc_delta
+#define vdso_calc_ns vdso_calc_ns
 
 #endif /* !__ASSEMBLY__ */
 
diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
index faccf12f7c03..9fa90e0794c9 100644
--- a/lib/vdso/gettimeofday.c
+++ b/lib/vdso/gettimeofday.c
@@ -5,23 +5,12 @@
 #include <vdso/datapage.h>
 #include <vdso/helpers.h>
 
-#ifndef vdso_calc_delta
+#ifndef vdso_calc_ns
 
 #ifdef VDSO_DELTA_NOMASK
-# define VDSO_DELTA_MASK(mask)	U64_MAX
+# define VDSO_DELTA_MASK(vd)	U64_MAX
 #else
-# define VDSO_DELTA_MASK(mask)	(mask)
-#endif
-
-/*
- * Default implementation which works for all sane clocksources. That
- * obviously excludes x86/TSC.
- */
-static __always_inline
-u64 vdso_calc_delta(u64 cycles, u64 last, u64 mask, u32 mult)
-{
-	return ((cycles - last) & VDSO_DELTA_MASK(mask)) * mult;
-}
+# define VDSO_DELTA_MASK(vd)	(vd->mask)
 #endif
 
 #ifndef vdso_shift_ns
@@ -31,6 +20,18 @@ static __always_inline u64 vdso_shift_ns(u64 ns, u32 shift)
 }
 #endif
 
+/*
+ * Default implementation which works for all sane clocksources. That
+ * obviously excludes x86/TSC.
+ */
+static __always_inline u64 vdso_calc_ns(const struct vdso_data *vd, u64 cycles, u64 base)
+{
+	u64 delta = (cycles - vd->cycle_last) & VDSO_DELTA_MASK(vd);
+
+	return vdso_shift_ns((delta * vd->mult) + base, vd->shift);
+}
+#endif /* vdso_calc_ns */
+
 #ifndef __arch_vdso_hres_capable
 static inline bool __arch_vdso_hres_capable(void)
 {
@@ -56,10 +57,10 @@ static inline bool vdso_cycles_ok(u64 cycles)
 static __always_inline int do_hres_timens(const struct vdso_data *vdns, clockid_t clk,
 					  struct __kernel_timespec *ts)
 {
-	const struct vdso_data *vd;
 	const struct timens_offset *offs = &vdns->offset[clk];
 	const struct vdso_timestamp *vdso_ts;
-	u64 cycles, last, ns;
+	const struct vdso_data *vd;
+	u64 cycles, ns;
 	u32 seq;
 	s64 sec;
 
@@ -80,10 +81,7 @@ static __always_inline int do_hres_timens(const struct vdso_data *vdns, clockid_
 		cycles = __arch_get_hw_counter(vd->clock_mode, vd);
 		if (unlikely(!vdso_cycles_ok(cycles)))
 			return -1;
-		ns = vdso_ts->nsec;
-		last = vd->cycle_last;
-		ns += vdso_calc_delta(cycles, last, vd->mask, vd->mult);
-		ns = vdso_shift_ns(ns, vd->shift);
+		ns = vdso_calc_ns(vd, cycles, vdso_ts->nsec);
 		sec = vdso_ts->sec;
 	} while (unlikely(vdso_read_retry(vd, seq)));
 
@@ -118,7 +116,7 @@ static __always_inline int do_hres(const struct vdso_data *vd, clockid_t clk,
 				   struct __kernel_timespec *ts)
 {
 	const struct vdso_timestamp *vdso_ts = &vd->basetime[clk];
-	u64 cycles, last, sec, ns;
+	u64 cycles, sec, ns;
 	u32 seq;
 
 	/* Allows to compile the high resolution parts out */
@@ -151,10 +149,7 @@ static __always_inline int do_hres(const struct vdso_data *vd, clockid_t clk,
 		cycles = __arch_get_hw_counter(vd->clock_mode, vd);
 		if (unlikely(!vdso_cycles_ok(cycles)))
 			return -1;
-		ns = vdso_ts->nsec;
-		last = vd->cycle_last;
-		ns += vdso_calc_delta(cycles, last, vd->mask, vd->mult);
-		ns = vdso_shift_ns(ns, vd->shift);
+		ns = vdso_calc_ns(vd, cycles, vdso_ts->nsec);
 		sec = vdso_ts->sec;
 	} while (unlikely(vdso_read_retry(vd, seq)));
 
-- 
2.34.1