Re: [dpdk-dev] [PATCH v2] timer: use rte_mp_msg to get freq from primary process

[Ye Xiaolong <xiaolong.ye@intel.com>]

On 08/21, Jim Harris wrote:
>Ideally, get_tsc_freq_arch() is able to provide the
>TSC rate using architecture-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.  So in secondary processes, if
>we cannot get the TSC rate using get_tsc_freq_arch(),
>try to get the TSC rate from the primary process
>instead using rte_mp_msg.  This is much faster than
>100ms.
>
>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.harris@intel.com>
>Change-Id: I584419ed1c7d6f47841e0a0eb23f34c9f1186d35

This Change-Id line is unnecessary.

Thanks,
Xiaolong

>---
> lib/librte_eal/common/eal_common_timer.c |   62 ++++++++++++++++++++++++++++++
> 1 file changed, 62 insertions(+)
>
>diff --git a/lib/librte_eal/common/eal_common_timer.c b/lib/librte_eal/common/eal_common_timer.c
>index 145543de7..ad965455d 100644
>--- a/lib/librte_eal/common/eal_common_timer.c
>+++ b/lib/librte_eal/common/eal_common_timer.c
>@@ -15,9 +15,17 @@
> #include <rte_log.h>
> #include <rte_cycles.h>
> #include <rte_pause.h>
>+#include <rte_eal.h>
>+#include <rte_errno.h>
> 
> #include "eal_private.h"
> 
>+#define EAL_TIMER_MP "eal_timer_mp_sync"
>+
>+struct timer_mp_param {
>+	uint64_t tsc_hz;
>+};
>+
> /* The frequency of the RDTSC timer resolution */
> static uint64_t eal_tsc_resolution_hz;
> 
>@@ -74,12 +82,58 @@ estimate_tsc_freq(void)
> 	return RTE_ALIGN_MUL_NEAR(rte_rdtsc() - start, CYC_PER_10MHZ);
> }
> 
>+static uint64_t
>+get_tsc_freq_from_primary(void)
>+{
>+	struct rte_mp_msg mp_req = {0};
>+	struct rte_mp_reply mp_reply = {0};
>+	struct timer_mp_param *r;
>+	struct timespec ts = {.tv_sec = 1, .tv_nsec = 0};
>+	uint64_t tsc_hz;
>+
>+	strcpy(mp_req.name, EAL_TIMER_MP);
>+	if (rte_mp_request_sync(&mp_req, &mp_reply, &ts) ||
>+	    mp_reply.nb_received != 1) {
>+		tsc_hz = 0;
>+	} else {
>+		r = (struct timer_mp_param *)mp_reply.msgs[0].param;
>+		tsc_hz = r->tsc_hz;
>+	}
>+
>+	free(mp_reply.msgs);
>+	return tsc_hz;
>+}
>+
>+static int
>+timer_mp_primary(__attribute__((unused)) const struct rte_mp_msg *msg,
>+		 const void *peer)
>+{
>+	struct rte_mp_msg reply = {0};
>+	struct timer_mp_param *r = (struct timer_mp_param *)reply.param;
>+
>+	r->tsc_hz = eal_tsc_resolution_hz;
>+	strcpy(reply.name, EAL_TIMER_MP);
>+	reply.len_param = sizeof(*r);
>+
>+	return rte_mp_reply(&reply, peer);
>+}
>+
> void
> set_tsc_freq(void)
> {
> 	uint64_t freq;
>+	int rc;
> 
> 	freq = get_tsc_freq_arch();
>+	if (!freq && rte_eal_process_type() != RTE_PROC_PRIMARY) {
>+		/* We couldn't get the TSC frequency through arch-specific
>+		 *  means.  If this is a secondary process, try to get the
>+		 *  TSC frequency from the primary process - this will
>+		 *  be much faster than get_tsc_freq() or estimate_tsc_freq()
>+		 *  below.
>+		 */
>+		freq = get_tsc_freq_from_primary();
>+	}
> 	if (!freq)
> 		freq = get_tsc_freq();
> 	if (!freq)
>@@ -87,6 +141,14 @@ 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) {
>+		rc = rte_mp_action_register(EAL_TIMER_MP, timer_mp_primary);
>+		if (rc && rte_errno != ENOTSUP) {
>+			RTE_LOG(WARNING, EAL, "Could not register mp_action - "
>+				"secondary processes will calculate TSC rate "
>+				"independently.\n");
>+		}
>+	}
> }
> 
> void rte_delay_us_callback_register(void (*userfunc)(unsigned int))
>