X-Git-Url: http://drtracing.org/?a=blobdiff_plain;f=arch%2Fx86%2Fkernel%2Ftsc.c;h=69b84a26ea17a215bbd7169af0148b176b40f242;hb=02386c356af0ce5bbee11ed9b23c312ca60298f0;hp=c3f7602cd0386b2fb0a1a7437263f9c71f27d03c;hpb=f73e22ab450140830005581c2c7ec389791a1b8d;p=deliverable%2Flinux.git

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index c3f7602cd038..69b84a26ea17 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -168,21 +168,20 @@ static void cyc2ns_write_end(int cpu, struct cyc2ns_data *data)
  *              ns = cycles * cyc2ns_scale / SC
  *
  *      And since SC is a constant power of two, we can convert the div
- *  into a shift.
+ *  into a shift. The larger SC is, the more accurate the conversion, but
+ *  cyc2ns_scale needs to be a 32-bit value so that 32-bit multiplication
+ *  (64-bit result) can be used.
  *
- *  We can use khz divisor instead of mhz to keep a better precision, since
- *  cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
+ *  We can use khz divisor instead of mhz to keep a better precision.
  *  (mathieu.desnoyers@polymtl.ca)
  *
  *                      -johnstul@us.ibm.com "math is hard, lets go shopping!"
  */
 
-#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
-
 static void cyc2ns_data_init(struct cyc2ns_data *data)
 {
 	data->cyc2ns_mul = 0;
-	data->cyc2ns_shift = CYC2NS_SCALE_FACTOR;
+	data->cyc2ns_shift = 0;
 	data->cyc2ns_offset = 0;
 	data->__count = 0;
 }
@@ -216,14 +215,14 @@ static inline unsigned long long cycles_2_ns(unsigned long long cyc)
 
 	if (likely(data == tail)) {
 		ns = data->cyc2ns_offset;
-		ns += mul_u64_u32_shr(cyc, data->cyc2ns_mul, CYC2NS_SCALE_FACTOR);
+		ns += mul_u64_u32_shr(cyc, data->cyc2ns_mul, data->cyc2ns_shift);
 	} else {
 		data->__count++;
 
 		barrier();
 
 		ns = data->cyc2ns_offset;
-		ns += mul_u64_u32_shr(cyc, data->cyc2ns_mul, CYC2NS_SCALE_FACTOR);
+		ns += mul_u64_u32_shr(cyc, data->cyc2ns_mul, data->cyc2ns_shift);
 
 		barrier();
 
@@ -257,12 +256,11 @@ static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
 	 * time function is continuous; see the comment near struct
 	 * cyc2ns_data.
 	 */
-	data->cyc2ns_mul =
-		DIV_ROUND_CLOSEST(NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR,
-				  cpu_khz);
-	data->cyc2ns_shift = CYC2NS_SCALE_FACTOR;
+	clocks_calc_mult_shift(&data->cyc2ns_mul, &data->cyc2ns_shift, cpu_khz,
+			       NSEC_PER_MSEC, 0);
+
 	data->cyc2ns_offset = ns_now -
-		mul_u64_u32_shr(tsc_now, data->cyc2ns_mul, CYC2NS_SCALE_FACTOR);
+		mul_u64_u32_shr(tsc_now, data->cyc2ns_mul, data->cyc2ns_shift);
 
 	cyc2ns_write_end(cpu, data);