sched/clock, x86: Rewrite cyc2ns() to avoid the need to disable IRQs

Use a ring-buffer like multi-version object structure which allows
always having a coherent object; we use this to avoid having to
disable IRQs while reading sched_clock() and avoids a problem when
getting an NMI while changing the cyc2ns data.

                        MAINLINE   PRE        POST

    sched_clock_stable: 1          1          1
    (cold) sched_clock: 329841     331312     257223
    (cold) local_clock: 301773     310296     309889
    (warm) sched_clock: 38375      38247      25280
    (warm) local_clock: 100371     102713     85268
    (warm) rdtsc:       27340      27289      24247
    sched_clock_stable: 0          0          0
    (cold) sched_clock: 382634     372706     301224
    (cold) local_clock: 396890     399275     399870
    (warm) sched_clock: 38194      38124      25630
    (warm) local_clock: 143452     148698     129629
    (warm) rdtsc:       27345      27365      24307

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-s567in1e5ekq2nlyhn8f987r@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 40 insertions, 26 deletions

diff --git a/arch/x86/platform/uv/tlb_uv.c b/arch/x86/platform/uv/tlb_uv.c
index efe4d7220397..dfe605ac1bcd 100644
--- a/arch/x86/platform/uv/tlb_uv.c
+++ b/arch/x86/platform/uv/tlb_uv.c
@@ -433,15 +433,49 @@ static void reset_with_ipi(struct pnmask *distribution, struct bau_control *bcp)
 	return;
 }
 
-static inline unsigned long cycles_2_us(unsigned long long cyc)
+/*
+ * Not to be confused with cycles_2_ns() from tsc.c; this gives a relative
+ * number, not an absolute. It converts a duration in cycles to a duration in
+ * ns.
+ */
+static inline unsigned long long cycles_2_ns(unsigned long long cyc)
 {
+	struct cyc2ns_data *data = cyc2ns_read_begin();
 	unsigned long long ns;
-	unsigned long us;
-	int cpu = smp_processor_id();
 
-	ns =  (cyc * per_cpu(cyc2ns, cpu)) >> CYC2NS_SCALE_FACTOR;
-	us = ns / 1000;
-	return us;
+	ns = mul_u64_u32_shr(cyc, data->cyc2ns_mul, data->cyc2ns_shift);
+
+	cyc2ns_read_end(data);
+	return ns;
+}
+
+/*
+ * The reverse of the above; converts a duration in ns to a duration in cycles.
+ */ 
+static inline unsigned long long ns_2_cycles(unsigned long long ns)
+{
+	struct cyc2ns_data *data = cyc2ns_read_begin();
+	unsigned long long cyc;
+
+	cyc = (ns << data->cyc2ns_shift) / data->cyc2ns_mul;
+
+	cyc2ns_read_end(data);
+	return cyc;
+}
+
+static inline unsigned long cycles_2_us(unsigned long long cyc)
+{
+	return cycles_2_ns(cyc) / NSEC_PER_USEC;
+}
+
+static inline cycles_t sec_2_cycles(unsigned long sec)
+{
+	return ns_2_cycles(sec * NSEC_PER_SEC);
+}
+
+static inline unsigned long long usec_2_cycles(unsigned long usec)
+{
+	return ns_2_cycles(usec * NSEC_PER_USEC);
 }
 
 /*
@@ -668,16 +702,6 @@ static int wait_completion(struct bau_desc *bau_desc,
 								bcp, try);
 }
 
-static inline cycles_t sec_2_cycles(unsigned long sec)
-{
-	unsigned long ns;
-	cycles_t cyc;
-
-	ns = sec * 1000000000;
-	cyc = (ns << CYC2NS_SCALE_FACTOR)/(per_cpu(cyc2ns, smp_processor_id()));
-	return cyc;
-}
-
 /*
  * Our retries are blocked by all destination sw ack resources being
  * in use, and a timeout is pending. In that case hardware immediately
@@ -1327,16 +1351,6 @@ static void ptc_seq_stop(struct seq_file *file, void *data)
 {
 }
 
-static inline unsigned long long usec_2_cycles(unsigned long microsec)
-{
-	unsigned long ns;
-	unsigned long long cyc;
-
-	ns = microsec * 1000;
-	cyc = (ns << CYC2NS_SCALE_FACTOR)/(per_cpu(cyc2ns, smp_processor_id()));
-	return cyc;
-}
-
 /*
  * Display the statistics thru /proc/sgi_uv/ptc_statistics
  * 'data' points to the cpu number