On Tue, 17 May 2022 11:01:15 +0100
Quentin Armitage <quen...@armitage.org.uk> wrote:
> 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: 8d23ce8f5ee ("pcapng: add new library for writing pcapng files")
> Cc: sta...@dpdk.org
>
> Signed-off-by: Quentin Armitage <quen...@armitage.org.uk>
> ---
> v2:
> - Don't call clock_gettime() in fast path
> - Update pcapng_time.ns and pcapng_time.cycles to ensure delta < tsc_hz
> - Stop using constructor to initialise pcapng_time.tsc_hz since
> it is not initialised until rte_eal_init() is called
> - use mean value of TSC before and after call to clock_gettime()
> - only call rte_get_tsc_hz() once
> - use rte_reciprocal functions instead of division
>
> lib/pcapng/rte_pcapng.c | 47 ++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 42 insertions(+), 5 deletions(-)
Side note: looked at an alternative using the timestamp offset option described
in the
PCAPNG IETF standard.
if_tsoffset:
The if_tsoffset option is a 64-bit signed integer value that
specifies an offset (in seconds) that must be added to the timestamp of
each packet to obtain the absolute timestamp of a packet. If the option
is missing, the timestamps stored in the packet MUST be considered
absolute timestamps. The time zone of the offset can be specified with
the option if_tzone.
But not supported even by current wireshark so not useful.
