From: Tyler Retzlaff <roretzla@linux.microsoft.com>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: dev@dpdk.org, Reshma Pattan <reshma.pattan@intel.com>
Subject: Re: [PATCH v3 3/5] latencystats: do not use floating point
Date: Wed, 17 Apr 2024 17:10:55 -0700 [thread overview]
Message-ID: <20240418001055.GC26881@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net> (raw)
In-Reply-To: <20240417170908.76701-4-stephen@networkplumber.org>
On Wed, Apr 17, 2024 at 10:07:25AM -0700, Stephen Hemminger wrote:
> The cycle counts do not need to be stored as floating point.
> Instead keep track of latency in cycles, and convert to
> nanoseconds when read.
>
> Change Exponential Weighted Moving Average weight from .2 to .25
> to avoid use of floating point for that.
>
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
> lib/latencystats/rte_latencystats.c | 37 +++++++++++------------------
> 1 file changed, 14 insertions(+), 23 deletions(-)
>
> diff --git a/lib/latencystats/rte_latencystats.c b/lib/latencystats/rte_latencystats.c
> index fe8c3c563a..11bd0ea4ae 100644
> --- a/lib/latencystats/rte_latencystats.c
> +++ b/lib/latencystats/rte_latencystats.c
> @@ -47,10 +47,10 @@ static uint64_t timer_tsc;
> static uint64_t prev_tsc;
>
> struct rte_latency_stats {
> - float min_latency; /**< Minimum latency in nano seconds */
> - float avg_latency; /**< Average latency in nano seconds */
> - float max_latency; /**< Maximum latency in nano seconds */
> - float jitter; /** Latency variation */
> + uint64_t min_latency; /**< Minimum latency */
> + uint64_t avg_latency; /**< Average latency */
> + uint64_t max_latency; /**< Maximum latency */
> + uint64_t jitter; /** Latency variation */
> rte_spinlock_t lock; /** Latency calculation lock */
> };
>
> @@ -82,13 +82,12 @@ int32_t
> rte_latencystats_update(void)
> {
> unsigned int i;
> - float *stats_ptr = NULL;
> uint64_t values[NUM_LATENCY_STATS] = {0};
> int ret;
>
> for (i = 0; i < NUM_LATENCY_STATS; i++) {
> - stats_ptr = RTE_PTR_ADD(glob_stats,
> - lat_stats_strings[i].offset);
> + const uint64_t *stats_ptr = RTE_PTR_ADD(glob_stats,
> + lat_stats_strings[i].offset);
> values[i] = floor(*stats_ptr / latencystat_cycles_per_ns());
will this need a cast to uint64_t?
> }
>
> @@ -105,11 +104,10 @@ static void
> rte_latencystats_fill_values(struct rte_metric_value *values)
> {
> unsigned int i;
> - float *stats_ptr = NULL;
>
> for (i = 0; i < NUM_LATENCY_STATS; i++) {
> - stats_ptr = RTE_PTR_ADD(glob_stats,
> - lat_stats_strings[i].offset);
> + const uint64_t *stats_ptr = RTE_PTR_ADD(glob_stats,
> + lat_stats_strings[i].offset);
> values[i].key = i;
> values[i].value = floor(*stats_ptr / latencystat_cycles_per_ns());
> }
> @@ -156,15 +154,8 @@ calc_latency(uint16_t pid __rte_unused,
> void *_ __rte_unused)
> {
> unsigned int i;
> - uint64_t now;
> - float latency;
> - static float prev_latency;
> - /*
> - * Alpha represents degree of weighting decrease in EWMA,
> - * a constant smoothing factor between 0 and 1. The value
> - * is used below for measuring average latency.
> - */
> - const float alpha = 0.2;
> + uint64_t now, latency;
> + static uint64_t prev_latency;
>
if this is merged i can abandon this series
https://patchwork.dpdk.org/project/dpdk/list/?series=31747
Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
next prev parent reply other threads:[~2024-04-18 0:10 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <0240408195036.182545-1-stephen@networkplumber.org>
2024-04-17 17:07 ` [PATCH v3 0/5] latencystats: cleanups Stephen Hemminger
2024-04-17 17:07 ` [PATCH v3 1/5] latencystats: replace use of VLA Stephen Hemminger
2024-04-17 18:03 ` Morten Brørup
2024-04-17 18:13 ` Stephen Hemminger
2024-04-18 0:00 ` Tyler Retzlaff
2024-04-17 17:07 ` [PATCH v3 2/5] latencystats: handle fractional cycles per ns Stephen Hemminger
2024-04-18 0:03 ` Tyler Retzlaff
2024-04-17 17:07 ` [PATCH v3 3/5] latencystats: do not use floating point Stephen Hemminger
2024-04-18 0:10 ` Tyler Retzlaff [this message]
2024-04-17 17:07 ` [PATCH v3 4/5] latencystats: fix log messages Stephen Hemminger
2024-04-18 0:13 ` Tyler Retzlaff
2024-04-17 17:07 ` [PATCH v3 5/5] latencystats: include file cleanup Stephen Hemminger
2024-04-17 17:30 ` Bruce Richardson
2024-04-17 18:13 ` Stephen Hemminger
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