[v2] net/pcap: support software Tx nanosecond timestamps
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Commit Message
When capturing packets into a PCAP file, DPDK currently uses
microseconds for the timestamps. But libpcap supports interpreting
tv_usec as nanoseconds depending on the file timestamp precision,
as of commit ba89e4a18e8b ("Make timestamps precision configurable").
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).
Note that NSEC_PER_SEC is defined as 1000000000L instead of 1e9 since
the latter might be interpreted as floating point.
Signed-off-by: Vivien Didelot <vivien.didelot@gmail.com>
---
doc/guides/rel_notes/release_20_08.rst | 6 ++++++
drivers/net/pcap/rte_eth_pcap.c | 15 ++++++++++++---
2 files changed, 18 insertions(+), 3 deletions(-)
Comments
Hi Stephen,
On Tue, 9 Jun 2020 12:43:57 -0700, Stephen Hemminger <stephen@networkplumber.org> wrote:
> On Tue, 9 Jun 2020 15:07:19 -0400
> Vivien Didelot <vivien.didelot@gmail.com> wrote:
>
> >
> > +#define NSEC_PER_SEC 1000000000L
> > +
> > 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;
> > + }
> > }
> >
>
> You may want to pre-compute the reciprocal here to save the expensive
> cost of divide in the fast path. See rte_reciprocal.
Please note that I did not change the calculation logic that was previously
used here. Thus pre-computing the reciprocal here to save the expensive cost
of divide in the fast path seems out of the scope of this patch to me.
Can we keep this for a future patch maybe?
Thanks,
Vivien
On 6/9/2020 8:57 PM, Vivien Didelot wrote:
> Hi Stephen,
>
> On Tue, 9 Jun 2020 12:43:57 -0700, Stephen Hemminger <stephen@networkplumber.org> wrote:
>> On Tue, 9 Jun 2020 15:07:19 -0400
>> Vivien Didelot <vivien.didelot@gmail.com> wrote:
>>
>>>
>>> +#define NSEC_PER_SEC 1000000000L
>>> +
>>> 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;
>>> + }
>>> }
>>>
>>
>> You may want to pre-compute the reciprocal here to save the expensive
>> cost of divide in the fast path. See rte_reciprocal.
>
> Please note that I did not change the calculation logic that was previously
> used here. Thus pre-computing the reciprocal here to save the expensive cost
> of divide in the fast path seems out of the scope of this patch to me.
>
> Can we keep this for a future patch maybe?
>
+1 to have this as incremental improvement to this patch.
On 6/9/2020 8:07 PM, Vivien Didelot wrote:
> When capturing packets into a PCAP file, DPDK currently uses
> microseconds for the timestamps. But libpcap supports interpreting
> tv_usec as nanoseconds depending on the file timestamp precision,
> as of commit ba89e4a18e8b ("Make timestamps precision configurable").
>
> 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).
>
> Note that NSEC_PER_SEC is defined as 1000000000L instead of 1e9 since
> the latter might be interpreted as floating point.
>
> Signed-off-by: Vivien Didelot <vivien.didelot@gmail.com>
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>
(Since there is a potential patch on top of this, I am merging this quickly)
Applied to dpdk-next-net/master, thanks.
@@ -56,6 +56,12 @@ New Features
Also, make sure to start the actual text at the margin.
=========================================================
+* **Updated PCAP driver.**
+
+ Updated PCAP driver with new features and improvements, including:
+
+ * Support software Tx nanosecond timestamps precision.
+
* **Updated Mellanox mlx5 driver.**
Updated Mellanox mlx5 driver with new features and improvements, including:
@@ -287,6 +287,8 @@ eth_null_rx(void *queue __rte_unused,
return 0;
}
+#define NSEC_PER_SEC 1000000000L
+
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;
+ }
}
/*
@@ -475,7 +483,8 @@ open_single_tx_pcap(const char *pcap_filename, pcap_dumper_t **dumper)
* with pcap_dump_open(). We create big enough an Ethernet
* pcap holder.
*/
- tx_pcap = pcap_open_dead(DLT_EN10MB, RTE_ETH_PCAP_SNAPSHOT_LEN);
+ tx_pcap = pcap_open_dead_with_tstamp_precision(DLT_EN10MB,
+ RTE_ETH_PCAP_SNAPSHOT_LEN, PCAP_TSTAMP_PRECISION_NANO);
if (tx_pcap == NULL) {
PMD_LOG(ERR, "Couldn't create dead pcap");
return -1;