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[204.195.112.199]) by smtp.gmail.com with ESMTPSA id l62-20020a639141000000b003c14af50625sm86016pge.61.2022.05.11.09.46.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 May 2022 09:46:58 -0700 (PDT) Date: Wed, 11 May 2022 09:46:55 -0700 From: Stephen Hemminger To: Quentin Armitage Cc: Reshma Pattan , Ray Kinsella , dev@dpdk.org, stable@dpdk.org Subject: Re: [PATCH] libpcapng: fix timestamp wrapping in output files Message-ID: <20220511094655.4f885c84@hermes.local> In-Reply-To: <20220507161237.207805-1-quentin@armitage.org.uk> References: <20220507161237.207805-1-quentin@armitage.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org On Sat, 7 May 2022 17:12:36 +0100 Quentin Armitage 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 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 #include #include +#include #include #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 */