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pcapng: fix timestamp wrapping in output files

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In pcap_tsc_to_ns(), delta * NSEC_PER_SEC will overflow approx 8
seconds after pcap_init is called when using a TSC with a frequency
of 2.5GHz.

To avoid the overflow, update the saved time and TSC value once
delta >= tsc_hz.

Fixes: 8d23ce8f5e ("pcapng: add new library for writing pcapng files")
Cc: stable@dpdk.org

Signed-off-by: Quentin Armitage <quentin@armitage.org.uk>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>
This commit is contained in:
Quentin Armitage 2022-05-17 11:01:15 +01:00 committed by Thomas Monjalon
parent d65c56c443
commit c882eb5448
1 changed files with 41 additions and 4 deletions
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45
lib/pcapng/rte_pcapng.c
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@ -19,6 +19,7 @@
#include <rte_ether.h>
#include <rte_mbuf.h>
#include <rte_pcapng.h>
#include <rte_reciprocal.h>
#include <rte_time.h>
#include "pcapng_proto.h"
@ -34,27 +35,63 @@ struct rte_pcapng {
};
/* For converting TSC cycles to PCAPNG ns format */
struct pcapng_time {
static struct pcapng_time {
uint64_t ns;
uint64_t cycles;
uint64_t tsc_hz;
struct rte_reciprocal_u64 tsc_hz_inverse;
} pcapng_time;
RTE_INIT(pcapng_init)
static inline void
pcapng_init(void)
{
struct timespec ts;
pcapng_time.cycles = rte_get_tsc_cycles();
clock_gettime(CLOCK_REALTIME, &ts);
pcapng_time.cycles = (pcapng_time.cycles + rte_get_tsc_cycles()) / 2;
pcapng_time.ns = rte_timespec_to_ns(&ts);
pcapng_time.tsc_hz = rte_get_tsc_hz();
pcapng_time.tsc_hz_inverse = rte_reciprocal_value_u64(pcapng_time.tsc_hz);
}
/* PCAPNG timestamps are in nanoseconds */
static uint64_t pcapng_tsc_to_ns(uint64_t cycles)
{
uint64_t delta;
uint64_t delta, secs;
if (!pcapng_time.tsc_hz)
pcapng_init();
/* In essence the calculation is:
* delta = (cycles - pcapng_time.cycles) * NSEC_PRE_SEC / rte_get_tsc_hz()
* but this overflows within 4 to 8 seconds depending on TSC frequency.
* Instead, if delta >= pcapng_time.tsc_hz:
* Increase pcapng_time.ns and pcapng_time.cycles by the number of
* whole seconds in delta and reduce delta accordingly.
* delta will therefore always lie in the interval [0, pcapng_time.tsc_hz),
* which will not overflow when multiplied by NSEC_PER_SEC provided the
* TSC frequency < approx 18.4GHz.
*
* Currently all TSCs operate below 5GHz.
*/
delta = cycles - pcapng_time.cycles;
return pcapng_time.ns + (delta * NSEC_PER_SEC) / rte_get_tsc_hz();
if (unlikely(delta >= pcapng_time.tsc_hz)) {
if (likely(delta < pcapng_time.tsc_hz * 2)) {
delta -= pcapng_time.tsc_hz;
pcapng_time.cycles += pcapng_time.tsc_hz;
pcapng_time.ns += NSEC_PER_SEC;
} else {
secs = rte_reciprocal_divide_u64(delta, &pcapng_time.tsc_hz_inverse);
delta -= secs * pcapng_time.tsc_hz;
pcapng_time.cycles += secs * pcapng_time.tsc_hz;
pcapng_time.ns += secs * NSEC_PER_SEC;
}
}
return pcapng_time.ns + rte_reciprocal_divide_u64(delta * NSEC_PER_SEC,
&pcapng_time.tsc_hz_inverse);
}
/* length of option including padding */