vdso: Consolidate nanoseconds calculation

Consolidate nanoseconds calculation to simplify and reduce code
duplication.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240325064023.2997-3-adrian.hunter@intel.com

Author: ahunter6

arch/x86/include/asm/vdso/gettimeofday.h

@@ -300,42 +300,41 @@ 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
  * the regular delta calculation (@cycles - @last) to return a huge time
  * 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
  * U64_MASK as an exception value, additionally arch_vdso_cycles_ok() above
  * 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__ */
 

lib/vdso/gettimeofday.c

@@ -5,31 +5,32 @@
 #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)
+# define VDSO_DELTA_MASK(vd)	(vd->mask)
+#endif
+
+#ifndef vdso_shift_ns
+static __always_inline u64 vdso_shift_ns(u64 ns, u32 shift)
+{
+	return ns >> shift;
+}
 #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)
+static __always_inline u64 vdso_calc_ns(const struct vdso_data *vd, u64 cycles, u64 base)
 {
-	return ((cycles - last) & VDSO_DELTA_MASK(mask)) * mult;
-}
-#endif
+	u64 delta = (cycles - vd->cycle_last) & VDSO_DELTA_MASK(vd);
 
-#ifndef vdso_shift_ns
-static __always_inline u64 vdso_shift_ns(u64 ns, u32 shift)
-{
-	return ns >> shift;
+	return vdso_shift_ns((delta * vd->mult) + base, vd->shift);
 }
-#endif
+#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)));