From: "Morten Brørup" <mb@smartsharesystems.com>
To: "Stephen Hemminger" <stephen@networkplumber.org>, <dev@dpdk.org>
Cc: "Reshma Pattan" <reshma.pattan@intel.com>
Subject: RE: [PATCH v3 1/5] latencystats: replace use of VLA
Date: Wed, 17 Apr 2024 20:03:55 +0200 [thread overview]
Message-ID: <98CBD80474FA8B44BF855DF32C47DC35E9F3B2@smartserver.smartshare.dk> (raw)
In-Reply-To: <20240417170908.76701-2-stephen@networkplumber.org>
> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> Sent: Wednesday, 17 April 2024 19.07
>
> The temporary array latencystats is not needed if the algorithm
> is converted into one pass.
>
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
> lib/latencystats/rte_latencystats.c | 31 +++++++++++++++--------------
> 1 file changed, 16 insertions(+), 15 deletions(-)
>
> diff --git a/lib/latencystats/rte_latencystats.c
> b/lib/latencystats/rte_latencystats.c
> index 4ea9b0d75b..9b345bfb33 100644
> --- a/lib/latencystats/rte_latencystats.c
> +++ b/lib/latencystats/rte_latencystats.c
> @@ -157,9 +157,9 @@ calc_latency(uint16_t pid __rte_unused,
> uint16_t nb_pkts,
> void *_ __rte_unused)
> {
> - unsigned int i, cnt = 0;
> + unsigned int i;
> uint64_t now;
> - float latency[nb_pkts];
> + float latency;
> static float prev_latency;
> /*
> * Alpha represents degree of weighting decrease in EWMA,
> @@ -169,13 +169,14 @@ calc_latency(uint16_t pid __rte_unused,
> const float alpha = 0.2;
>
> now = rte_rdtsc();
> - for (i = 0; i < nb_pkts; i++) {
> - if (pkts[i]->ol_flags & timestamp_dynflag)
> - latency[cnt++] = now - *timestamp_dynfield(pkts[i]);
> - }
>
> rte_spinlock_lock(&glob_stats->lock);
> - for (i = 0; i < cnt; i++) {
> + for (i = 0; i < nb_pkts; i++) {
> + if (!(pkts[i]->ol_flags & timestamp_dynflag))
> + continue;
> +
> + latency = now - *timestamp_dynfield(pkts[i]);
> +
> /*
> * The jitter is calculated as statistical mean of
> interpacket
> * delay variation. The "jitter estimate" is computed by
> taking
> @@ -187,22 +188,22 @@ calc_latency(uint16_t pid __rte_unused,
> * Reference: Calculated as per RFC 5481, sec 4.1,
> * RFC 3393 sec 4.5, RFC 1889 sec.
> */
> - glob_stats->jitter += (fabsf(prev_latency - latency[i])
> + glob_stats->jitter += (fabsf(prev_latency - latency)
> - glob_stats->jitter)/16;
> if (glob_stats->min_latency == 0)
You could add unlikely() to this comparison. It should only happen once in a lifetime.
> - glob_stats->min_latency = latency[i];
> - else if (latency[i] < glob_stats->min_latency)
> - glob_stats->min_latency = latency[i];
> - else if (latency[i] > glob_stats->max_latency)
> - glob_stats->max_latency = latency[i];
> + glob_stats->min_latency = latency;
In theory, glob_stats->max_latency should also be initialized with the first sample value here.
> + else if (latency < glob_stats->min_latency)
> + glob_stats->min_latency = latency;
> + else if (latency > glob_stats->max_latency)
> + glob_stats->max_latency = latency;
The min/max comparisons are also unlikely.
> /*
> * The average latency is measured using exponential moving
> * average, i.e. using EWMA
> * https://en.wikipedia.org/wiki/Moving_average
> */
> glob_stats->avg_latency +=
> - alpha * (latency[i] - glob_stats->avg_latency);
> - prev_latency = latency[i];
> + alpha * (latency - glob_stats->avg_latency);
> + prev_latency = latency;
> }
> rte_spinlock_unlock(&glob_stats->lock);
>
> --
> 2.43.0
With or without suggested changes,
Acked-by: Morten Brørup <mb@smartsharesystems.com>
next prev parent reply other threads:[~2024-04-17 18:04 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 [this message]
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
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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