[dpdk-dev] [PATCH 1/2] net/pcap: support software Tx nanosecond timestamp
Stephen Hemminger
stephen at networkplumber.org
Sun May 24 03:39:50 CEST 2020
On Sat, 23 May 2020 13:21:29 -0400
Vivien Didelot <vivien.didelot at gmail.com> wrote:
> When capturing packets into a PCAP file, DPDK currently uses
> microseconds for the timestamp. But libpcap supports interpreting
> tv_usec as nanoseconds depending on the file timestamp precision.
>
> To support this, use PCAP_TSTAMP_PRECISION_NANO when creating the
> empty PCAP file as specified by PCAP_OPEN_DEAD(3PCAP) and implement
> nanosecond timeval addition. This also ensures that the precision
> reported by capinfos is nanoseconds (9).
>
> Signed-off-by: Vivien Didelot <vivien.didelot at gmail.com>
> ---
> drivers/net/pcap/rte_eth_pcap.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/pcap/rte_eth_pcap.c b/drivers/net/pcap/rte_eth_pcap.c
> index b4c79d174..68588c3d7 100644
> --- a/drivers/net/pcap/rte_eth_pcap.c
> +++ b/drivers/net/pcap/rte_eth_pcap.c
> @@ -287,6 +287,8 @@ eth_null_rx(void *queue __rte_unused,
> return 0;
> }
>
> +#define NSEC_PER_SEC 1e9
> +
> static inline void
> calculate_timestamp(struct timeval *ts) {
> uint64_t cycles;
> @@ -294,8 +296,14 @@ calculate_timestamp(struct timeval *ts) {
>
> cycles = rte_get_timer_cycles() - start_cycles;
> cur_time.tv_sec = cycles / hz;
> - cur_time.tv_usec = (cycles % hz) * 1e6 / hz;
> - timeradd(&start_time, &cur_time, ts);
> + cur_time.tv_usec = (cycles % hz) * NSEC_PER_SEC / hz;
> +
> + ts->tv_sec = start_time.tv_sec + cur_time.tv_sec;
> + ts->tv_usec = start_time.tv_usec + cur_time.tv_usec;
> + if (ts->tv_usec > NSEC_PER_SEC) {
> + ts->tv_usec -= NSEC_PER_SEC;
> + ts->tv_sec += 1;
> + }
Please no floating point math in the fast path of capturing packets!
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