From: Stephen Hemminger <stephen@networkplumber.org> To: Quentin Armitage <quentin@armitage.org.uk> Cc: Reshma Pattan <reshma.pattan@intel.com>, Ray Kinsella <mdr@ashroe.eu>, dev@dpdk.org, stable@dpdk.org Subject: Re: [PATCH] libpcapng: fix timestamp wrapping in output files Date: Wed, 11 May 2022 09:46:55 -0700 Message-ID: <20220511094655.4f885c84@hermes.local> (raw) In-Reply-To: <20220507161237.207805-1-quentin@armitage.org.uk> On Sat, 7 May 2022 17:12:36 +0100 Quentin Armitage <quentin@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, reread the time and TSC once > delta * NSEC_PER_SEC > (1 << 63). In order to ensure that there > is no overflow if there is a several second gap between calls to > pcapng_tsc_to_ns() the actual check to reread the clock is: > delta > ((1ULL << 63) / NSEC_PER_SEC) > > Fixes: 8d23ce8f5ee ("pcapng: add new library for writing pcapng files") > Cc: stable@dpdk.org > > Signed-off-by: Quentin Armitage <quentin@armitage.org.uk> What about something like this instead. diff --git a/lib/pcapng/rte_pcapng.c b/lib/pcapng/rte_pcapng.c index 90b2f5bc6905..c5534301bf2c 100644 --- a/lib/pcapng/rte_pcapng.c +++ b/lib/pcapng/rte_pcapng.c @@ -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 +35,39 @@ struct rte_pcapng { }; /* For converting TSC cycles to PCAPNG ns format */ -struct pcapng_time { +#define TICK_SCALE 16u +static struct { uint64_t ns; uint64_t cycles; + struct rte_reciprocal_u64 inverse; } pcapng_time; RTE_INIT(pcapng_init) { struct timespec ts; + uint64_t scale_tick_per_ns; pcapng_time.cycles = rte_get_tsc_cycles(); clock_gettime(CLOCK_REALTIME, &ts); pcapng_time.ns = rte_timespec_to_ns(&ts); + + scale_tick_per_ns = (rte_get_tsc_hz() * TICK_SCALE) / NSEC_PER_SEC; + pcapng_time.inverse = rte_reciprocal_value_u64(scale_tick_per_ns); } /* PCAPNG timestamps are in nanoseconds */ static uint64_t pcapng_tsc_to_ns(uint64_t cycles) { - uint64_t delta; + uint64_t delta, elapsed; delta = cycles - pcapng_time.cycles; - return pcapng_time.ns + (delta * NSEC_PER_SEC) / rte_get_tsc_hz(); + + /* Compute elapsed time in nanoseconds scaled by TICK_SCALE + * since the start of the capture. + * With scale of 4 this will roll over in 36 years. + */ + elapsed = rte_reciprocal_divide_u64(delta, &pcapng_time.inverse); + return pcapng_time.ns + elapsed / TICK_SCALE; } /* length of option including padding */
next prev parent reply other threads:[~2022-05-11 16:47 UTC|newest] Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-05-07 16:12 Quentin Armitage 2022-05-11 16:08 ` Stephen Hemminger 2022-05-11 16:46 ` Stephen Hemminger [this message] 2022-05-14 17:14 ` Quentin Armitage 2022-05-16 13:26 ` Stephen Hemminger 2022-05-17 10:01 ` [PATCH v2] " Quentin Armitage 2022-05-17 15:15 ` Stephen Hemminger 2022-06-01 14:38 ` Thomas Monjalon 2022-05-17 21:04 ` Stephen Hemminger
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20220511094655.4f885c84@hermes.local \ --to=stephen@networkplumber.org \ --cc=dev@dpdk.org \ --cc=mdr@ashroe.eu \ --cc=quentin@armitage.org.uk \ --cc=reshma.pattan@intel.com \ --cc=stable@dpdk.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
patches for DPDK stable branches This inbox may be cloned and mirrored by anyone: git clone --mirror http://inbox.dpdk.org/stable/0 stable/git/0.git # If you have public-inbox 1.1+ installed, you may # initialize and index your mirror using the following commands: public-inbox-init -V2 stable stable/ http://inbox.dpdk.org/stable \ stable@dpdk.org public-inbox-index stable Example config snippet for mirrors. Newsgroup available over NNTP: nntp://inbox.dpdk.org/inbox.dpdk.stable AGPL code for this site: git clone https://public-inbox.org/public-inbox.git