[dpdk-dev] [PATCH v2] net/pcap: support software Tx nanosecond timestamps

[dpdk-dev] [PATCH v2] net/pcap: support software Tx nanosecond timestamps

[Vivien Didelot]

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(-)

diff --git a/doc/guides/rel_notes/release_20_08.rst b/doc/guides/rel_notes/release_20_08.rst
index dee4ccbb5..7a67c960c 100644
--- a/doc/guides/rel_notes/release_20_08.rst
+++ b/doc/guides/rel_notes/release_20_08.rst
@@ -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:
diff --git a/drivers/net/pcap/rte_eth_pcap.c b/drivers/net/pcap/rte_eth_pcap.c
index b4c79d174..13a3d0ac7 100644
--- a/drivers/net/pcap/rte_eth_pcap.c
+++ b/drivers/net/pcap/rte_eth_pcap.c
@@ -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;
-- 
2.27.0

Re: [dpdk-dev] [PATCH v2] net/pcap: support software Tx nanosecond timestamps

[Stephen Hemminger]

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.

Re: [dpdk-dev] [PATCH v2] net/pcap: support software Tx nanosecond timestamps

[Vivien Didelot]

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

Re: [dpdk-dev] [PATCH v2] net/pcap: support software Tx nanosecond timestamps

[Ferruh Yigit]

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.

Re: [dpdk-dev] [PATCH v2] net/pcap: support software Tx nanosecond timestamps

[Ferruh Yigit]

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.