[dpdk-dev] [PATCH v4] eal: use memzone to share tsc hz with secondary processes

[Jim Harris]

Ideally, get_tsc_freq_arch() is able to provide the
TSC rate using arch-specific means.  When that is not
possible, DPDK reverts to calculating the TSC rate with
a 100ms nanosleep or 1s sleep.  The latter occurs more
frequently in VMs which often do not have access to the
data they need from arch-specific means (CPUID leaf 0x15
or MSR 0xCE on x86).

In secondary processes, the extra 100ms is especially
noticeable and consumes the bulk of rte_eal_init()
execution time.  To resolve this extra delay, have
the primary process put the TSC rate into a shared
memory region that the secondary process can lookup.

Reduces rte_eal_init() execution time in a secondary
process from 165ms to 66ms on my test system.

Signed-off-by: Jim Harris <james.r.har...@intel.com>
---
 lib/librte_eal/common/eal_common_timer.c |   24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/lib/librte_eal/common/eal_common_timer.c 
b/lib/librte_eal/common/eal_common_timer.c
index 145543de7..b2c813444 100644
--- a/lib/librte_eal/common/eal_common_timer.c
+++ b/lib/librte_eal/common/eal_common_timer.c
@@ -15,9 +15,12 @@
 #include <rte_log.h>
 #include <rte_cycles.h>
 #include <rte_pause.h>
+#include <rte_memzone.h>
 
 #include "eal_private.h"
 
+static const char *MZ_RTE_TSC_FREQ = "rte_tsc_freq";
+
 /* The frequency of the RDTSC timer resolution */
 static uint64_t eal_tsc_resolution_hz;
 
@@ -77,9 +80,17 @@ estimate_tsc_freq(void)
 void
 set_tsc_freq(void)
 {
-       uint64_t freq;
-
-       freq = get_tsc_freq_arch();
+       const struct rte_memzone *mz;
+       uint64_t freq = 0;
+
+       if (rte_eal_process_type() == RTE_PROC_SECONDARY) {
+               mz = rte_memzone_lookup(MZ_RTE_TSC_FREQ);
+               if (mz != NULL) {
+                       freq = *(uint64_t *)mz->addr;
+               }
+       }
+       if (!freq)
+               freq = get_tsc_freq_arch();
        if (!freq)
                freq = get_tsc_freq();
        if (!freq)
@@ -87,6 +98,13 @@ set_tsc_freq(void)
 
        RTE_LOG(DEBUG, EAL, "TSC frequency is ~%" PRIu64 " KHz\n", freq / 1000);
        eal_tsc_resolution_hz = freq;
+       if (rte_eal_process_type() == RTE_PROC_PRIMARY) {
+               mz = rte_memzone_reserve(MZ_RTE_TSC_FREQ, sizeof(uint64_t),
+                                        SOCKET_ID_ANY, 0);
+               if (mz != NULL) {
+                       *(uint64_t *)mz->addr = freq;
+               }
+       }
 }
 
 void rte_delay_us_callback_register(void (*userfunc)(unsigned int))