[PATCH v3 2/2] timer/linux/x86: override TSC freq if no tsc_known_freq

[Isaac Boukris <iboukris@gmail.com>]

If the tsc_known_freq cpu flag is missing, it means the kernel doesn't
trust it and calculates its own. We should do the same to avoid drift.

Signed-off-by: Isaac Boukris <iboukris@gmail.com>
---
 lib/eal/common/eal_common_timer.c |  3 +-
 lib/eal/common/eal_private.h      |  2 +-
 lib/eal/freebsd/eal_timer.c       |  5 ++-
 lib/eal/linux/eal_timer.c         | 53 +++++++++++++++++++++++++++++--
 lib/eal/windows/eal_timer.c       |  5 ++-
 5 files changed, 60 insertions(+), 8 deletions(-)

diff --git a/lib/eal/common/eal_common_timer.c b/lib/eal/common/eal_common_timer.c
index c5c4703f15..e00be0a5c8 100644
--- a/lib/eal/common/eal_common_timer.c
+++ b/lib/eal/common/eal_common_timer.c
@@ -66,8 +66,7 @@ set_tsc_freq(void)
 	}
 
 	freq = get_tsc_freq_arch();
-	if (!freq)
-		freq = get_tsc_freq();
+	freq = get_tsc_freq(freq);
 	if (!freq)
 		freq = estimate_tsc_freq();
 
diff --git a/lib/eal/common/eal_private.h b/lib/eal/common/eal_private.h
index af09620426..bb315dab04 100644
--- a/lib/eal/common/eal_private.h
+++ b/lib/eal/common/eal_private.h
@@ -374,7 +374,7 @@ void set_tsc_freq(void);
  *
  * This function is private to the EAL.
  */
-uint64_t get_tsc_freq(void);
+uint64_t get_tsc_freq(uint64_t arch_hz);
 
 /**
  * Get TSC frequency if the architecture supports.
diff --git a/lib/eal/freebsd/eal_timer.c b/lib/eal/freebsd/eal_timer.c
index 3dd70e24ba..5a8aea03e1 100644
--- a/lib/eal/freebsd/eal_timer.c
+++ b/lib/eal/freebsd/eal_timer.c
@@ -26,12 +26,15 @@
 enum timer_source eal_timer_source = EAL_TIMER_TSC;
 
 uint64_t
-get_tsc_freq(void)
+get_tsc_freq(uint64_t arch_hz)
 {
 	size_t sz;
 	int tmp;
 	uint64_t tsc_hz;
 
+	if (arch_hz)
+		return arch_hz;
+
 	sz = sizeof(tmp);
 	tmp = 0;
 
diff --git a/lib/eal/linux/eal_timer.c b/lib/eal/linux/eal_timer.c
index f56a7ae15b..2c5fc9ff3e 100644
--- a/lib/eal/linux/eal_timer.c
+++ b/lib/eal/linux/eal_timer.c
@@ -5,9 +5,9 @@
 
 #include <stdio.h>
 #include <stdint.h>
+#include <inttypes.h>
 #ifdef RTE_LIBEAL_USE_HPET
 #include <fcntl.h>
-#include <inttypes.h>
 #include <sys/mman.h>
 #include <unistd.h>
 #endif
@@ -187,8 +187,41 @@ rte_eal_hpet_init(int make_default)
 }
 #endif
 
+/* Check if the kernel deems the arch provided TSC frequency trustworthy. */
+
+static bool
+is_tsc_known_freq(void)
+{
+	bool ret = true; /* Assume tsc_known_freq */
+
+#if defined(RTE_ARCH_X86)
+	char line[2048];
+	FILE *stream;
+
+	stream = fopen("/proc/cpuinfo", "r");
+	if (!stream) {
+		EAL_LOG(WARNING, "Unable to open /proc/cpuinfo");
+		return ret;
+	}
+
+	while (fgets(line, sizeof(line), stream)) {
+		if (strncmp(line, "flags", 5) != 0)
+			continue;
+
+		if (!strstr(line, "tsc_known_freq"))
+			ret = false;
+
+		break;
+	}
+
+	fclose(stream);
+#endif
+
+	return ret;
+}
+
 uint64_t
-get_tsc_freq(void)
+get_tsc_freq(uint64_t arch_hz)
 {
 #ifdef CLOCK_MONOTONIC_RAW
 #define NS_PER_SEC 1E9
@@ -199,6 +232,9 @@ get_tsc_freq(void)
 	struct timespec t_start, t_end;
 	uint64_t tsc_hz;
 
+	if (arch_hz && is_tsc_known_freq())
+		return arch_hz;
+
 	if (clock_gettime(CLOCK_MONOTONIC_RAW, &t_start) == 0) {
 		uint64_t ns, end, start = rte_rdtsc();
 		nanosleep(&sleeptime,NULL);
@@ -209,11 +245,22 @@ get_tsc_freq(void)
 
 		double secs = (double)ns/NS_PER_SEC;
 		tsc_hz = (uint64_t)((end - start)/secs);
+
+		if (arch_hz) {
+			/* Make sure we're within 1% for sanity check */
+			if (arch_hz - tsc_hz > arch_hz / 100)
+				return arch_hz;
+
+			EAL_LOG(DEBUG,
+				"Refined arch frequency %"PRIu64" to measured frequency %"PRIu64,
+				arch_hz, tsc_hz);
+		}
+
 		/* Round up to 100Khz. 1E5 ~ 100Khz */
 		return RTE_ALIGN_MUL_NEAR(tsc_hz, CYC_PER_100KHZ);
 	}
 #endif
-	return 0;
+	return arch_hz;
 }
 
 int
diff --git a/lib/eal/windows/eal_timer.c b/lib/eal/windows/eal_timer.c
index b070cb7751..cfd6c267ac 100644
--- a/lib/eal/windows/eal_timer.c
+++ b/lib/eal/windows/eal_timer.c
@@ -49,13 +49,16 @@ rte_delay_us_sleep(unsigned int us)
 }
 
 uint64_t
-get_tsc_freq(void)
+get_tsc_freq(uint64_t arch_hz)
 {
 	LARGE_INTEGER t_start, t_end, elapsed_us;
 	LARGE_INTEGER frequency;
 	uint64_t tsc_hz;
 	uint64_t end, start;
 
+	if (arch_hz)
+		return arch_hz;
+
 	QueryPerformanceFrequency(&frequency);
 
 	QueryPerformanceCounter(&t_start);
-- 
2.45.0