diff mbox series

latencystats: fix timestamp marking and latency calculation

Message ID 1537545703-9599-1-git-send-email-reshma.pattan@intel.com (mailing list archive)
State Superseded, archived
Delegated to: Thomas Monjalon
Headers
Series latencystats: fix timestamp marking and latency calculation |

Checks

Context Check Description
ci/checkpatch success coding style OK
ci/Intel-compilation success Compilation OK

Commit Message

Pattan, Reshma Sept. 21, 2018, 4:01 p.m. UTC 
  Latency calculation logic is not correct for the case where
packets gets dropped before TX. As for the dropped packets,
the timestamp is not cleared, and such packets still gets
counted for latency calculation in next runs, that will result
in inaccurate latency measurement.

So fix this issue as below,

Before setting timestamp in mbuf, check mbuf don't have
any prior valid time stamp flag set and after marking
the timestamp, set mbuf flags to indicate timestamp is
valid.

Before calculating timestamp check mbuf flags are set to
indicate timestamp is valid.

With the above logic it is guaranteed that correct timestamps
have been used.

Fixes: 5cd3cac9ed ("latency: added new library for latency stats")

Reported-by: Bao-Long Tran <longtb5@viettel.com.vn>
Signed-off-by: Reshma Pattan <reshma.pattan@intel.com>
---
 lib/librte_latencystats/rte_latencystats.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

Comments

longtb5@viettel.com.vn Sept. 22, 2018, 2:58 a.m. UTC | #1 
Hi Reshma,

> -----Original Message-----
> From: reshma.pattan@intel.com [mailto:reshma.pattan@intel.com]
> Sent: Friday, September 21, 2018 11:02 PM
> To: longtb5@viettel.com.vn; konstantin.ananyev@intel.com; dev@dpdk.org
> Cc: Reshma Pattan <reshma.pattan@intel.com>
> Subject: [PATCH] latencystats: fix timestamp marking and latency
calculation
> 
> Latency calculation logic is not correct for the case where packets gets
> dropped before TX. As for the dropped packets, the timestamp is not
> cleared, and such packets still gets counted for latency calculation in
next
> runs, that will result in inaccurate latency measurement.
> 
> So fix this issue as below,
> 
> Before setting timestamp in mbuf, check mbuf don't have any prior valid
> time stamp flag set and after marking the timestamp, set mbuf flags to
> indicate timestamp is valid.
> 
> Before calculating timestamp check mbuf flags are set to indicate
timestamp
> is valid.
> 

This solution as suggested by Konstantin is great. Not only does it solve
the problem but also now the usage of mbuf->timestamp is not exclusive to
latencystats anymore. The application can make use of timestamp at the same
as latencystats simply by toggling PKT_RX_TIMESTAMP. I think we should
update the doc to include this information. 

> With the above logic it is guaranteed that correct timestamps have been
> used.
> 
> Fixes: 5cd3cac9ed ("latency: added new library for latency stats")
> 
> Reported-by: Bao-Long Tran <longtb5@viettel.com.vn>
> Signed-off-by: Reshma Pattan <reshma.pattan@intel.com>
> ---
>  lib/librte_latencystats/rte_latencystats.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/librte_latencystats/rte_latencystats.c
> b/lib/librte_latencystats/rte_latencystats.c
> index 1fdec68e3..8870226bb 100644
> --- a/lib/librte_latencystats/rte_latencystats.c
> +++ b/lib/librte_latencystats/rte_latencystats.c
> @@ -125,8 +125,11 @@ add_time_stamps(uint16_t pid __rte_unused,
>  	for (i = 0; i < nb_pkts; i++) {
>  		diff_tsc = now - prev_tsc;
>  		timer_tsc += diff_tsc;
> -		if (timer_tsc >= samp_intvl) {
> +
> +		if ((pkts[i]->ol_flags & PKT_RX_TIMESTAMP) == 0
> +			&& (timer_tsc >= samp_intvl)) {
>  			pkts[i]->timestamp = now;
> +			pkts[i]->ol_flags |= PKT_RX_TIMESTAMP;
>  			timer_tsc = 0;
>  		}
>  		prev_tsc = now;
> @@ -156,7 +159,8 @@ calc_latency(uint16_t pid __rte_unused,
> 
>  	now = rte_rdtsc();
>  	for (i = 0; i < nb_pkts; i++) {
> -		if (pkts[i]->timestamp)
> +		if ((pkts[i]->ol_flags & PKT_RX_TIMESTAMP) &&
> +				pkts[i]->timestamp)

Just a nit, but I think we don't have to check for pkts[i]->timestamp here.

>  			latency[cnt++] = now - pkts[i]->timestamp;
>  	}
> 
> --
> 2.14.4

Best regards,
BL
longtb5@viettel.com.vn Sept. 24, 2018, 7:10 a.m. UTC | #2 
> -----Original Message-----
> From: reshma.pattan@intel.com [mailto:reshma.pattan@intel.com]
> Sent: Friday, September 21, 2018 11:02 PM
> To: longtb5@viettel.com.vn; konstantin.ananyev@intel.com; dev@dpdk.org
> Cc: Reshma Pattan <reshma.pattan@intel.com>
> Subject: [PATCH] latencystats: fix timestamp marking and latency
calculation
> 
> Latency calculation logic is not correct for the case where packets gets
> dropped before TX. As for the dropped packets, the timestamp is not
> cleared, and such packets still gets counted for latency calculation in
next
> runs, that will result in inaccurate latency measurement.
> 
> So fix this issue as below,
> 
> Before setting timestamp in mbuf, check mbuf don't have any prior valid
> time stamp flag set and after marking the timestamp, set mbuf flags to
> indicate timestamp is valid.
> 
> Before calculating timestamp check mbuf flags are set to indicate
timestamp
> is valid.
> 
> With the above logic it is guaranteed that correct timestamps have been
> used.
> 
> Fixes: 5cd3cac9ed ("latency: added new library for latency stats")
> 
> Reported-by: Bao-Long Tran <longtb5@viettel.com.vn>
> Signed-off-by: Reshma Pattan <reshma.pattan@intel.com>

Tested-by: Bao-Long Tran <longtb5@viettel.com.vn>
Pattan, Reshma Sept. 24, 2018, 1:07 p.m. UTC | #3 
Hi,

> -----Original Message-----
> From: longtb5@viettel.com.vn [mailto:longtb5@viettel.com.vn]
> Sent: Saturday, September 22, 2018 3:58 AM
> To: Pattan, Reshma <reshma.pattan@intel.com>; Ananyev, Konstantin
> <konstantin.ananyev@intel.com>; dev@dpdk.org
> Subject: RE: [PATCH] latencystats: fix timestamp marking and latency
> calculation
> 
> Hi Reshma,
> 
> > -----Original Message-----
> > From: reshma.pattan@intel.com [mailto:reshma.pattan@intel.com]
> > Sent: Friday, September 21, 2018 11:02 PM
> > To: longtb5@viettel.com.vn; konstantin.ananyev@intel.com;
> dev@dpdk.org
> > Cc: Reshma Pattan <reshma.pattan@intel.com>
> > Subject: [PATCH] latencystats: fix timestamp marking and latency
> calculation
> >
> > Latency calculation logic is not correct for the case where packets
> > gets dropped before TX. As for the dropped packets, the timestamp is
> > not cleared, and such packets still gets counted for latency
> > calculation in
> next
> > runs, that will result in inaccurate latency measurement.
> >
> > So fix this issue as below,
> >
> > Before setting timestamp in mbuf, check mbuf don't have any prior
> > valid time stamp flag set and after marking the timestamp, set mbuf
> > flags to indicate timestamp is valid.
> >
> > Before calculating timestamp check mbuf flags are set to indicate
> timestamp
> > is valid.
> >
> 
> This solution as suggested by Konstantin is great. Not only does it solve the
> problem but also now the usage of mbuf->timestamp is not exclusive to
> latencystats anymore. The application can make use of timestamp at the
> same as latencystats simply by toggling PKT_RX_TIMESTAMP. I think we
> should update the doc to include this information.
> 

Do you mean latency stats document? Or Mbuf doc.  

Thanks,
Reshma
longtb5@viettel.com.vn Sept. 25, 2018, 3:22 p.m. UTC | #4 
Hi Reshma,

I mean in the latencystats document. A few lines about what is taken away
by the library (the mbuf timestamp when PKT_RX_TIMESTAMP is set) would be
very helpful.

Best regards,
BL

----- Original Message -----
From: "reshma pattan" <reshma.pattan@intel.com>
To: longtb5@viettel.com.vn
Cc: "Konstantin Ananyev" <konstantin.ananyev@intel.com>, dev@dpdk.org
Sent: Monday, September 24, 2018 8:07:18 PM
Subject: RE: [PATCH] latencystats: fix timestamp marking and latency calculation

Hi,

> -----Original Message-----
> From: longtb5@viettel.com.vn [mailto:longtb5@viettel.com.vn]
> Sent: Saturday, September 22, 2018 3:58 AM
> To: Pattan, Reshma <reshma.pattan@intel.com>; Ananyev, Konstantin
> <konstantin.ananyev@intel.com>; dev@dpdk.org
> Subject: RE: [PATCH] latencystats: fix timestamp marking and latency
> calculation
> 
> Hi Reshma,
> 
> > -----Original Message-----
> > From: reshma.pattan@intel.com [mailto:reshma.pattan@intel.com]
> > Sent: Friday, September 21, 2018 11:02 PM
> > To: longtb5@viettel.com.vn; konstantin.ananyev@intel.com;
> dev@dpdk.org
> > Cc: Reshma Pattan <reshma.pattan@intel.com>
> > Subject: [PATCH] latencystats: fix timestamp marking and latency
> calculation
> >
> > Latency calculation logic is not correct for the case where packets
> > gets dropped before TX. As for the dropped packets, the timestamp is
> > not cleared, and such packets still gets counted for latency
> > calculation in
> next
> > runs, that will result in inaccurate latency measurement.
> >
> > So fix this issue as below,
> >
> > Before setting timestamp in mbuf, check mbuf don't have any prior
> > valid time stamp flag set and after marking the timestamp, set mbuf
> > flags to indicate timestamp is valid.
> >
> > Before calculating timestamp check mbuf flags are set to indicate
> timestamp
> > is valid.
> >
> 
> This solution as suggested by Konstantin is great. Not only does it solve the
> problem but also now the usage of mbuf->timestamp is not exclusive to
> latencystats anymore. The application can make use of timestamp at the
> same as latencystats simply by toggling PKT_RX_TIMESTAMP. I think we
> should update the doc to include this information.
> 

Do you mean latency stats document? Or Mbuf doc.  

Thanks,
Reshma
diff mbox series

Patch

diff --git a/lib/librte_latencystats/rte_latencystats.c b/lib/librte_latencystats/rte_latencystats.c
index 1fdec68e3..8870226bb 100644
--- a/lib/librte_latencystats/rte_latencystats.c
+++ b/lib/librte_latencystats/rte_latencystats.c
@@ -125,8 +125,11 @@  add_time_stamps(uint16_t pid __rte_unused,
 	for (i = 0; i < nb_pkts; i++) {
 		diff_tsc = now - prev_tsc;
 		timer_tsc += diff_tsc;
-		if (timer_tsc >= samp_intvl) {
+
+		if ((pkts[i]->ol_flags & PKT_RX_TIMESTAMP) == 0
+			&& (timer_tsc >= samp_intvl)) {
 			pkts[i]->timestamp = now;
+			pkts[i]->ol_flags |= PKT_RX_TIMESTAMP;
 			timer_tsc = 0;
 		}
 		prev_tsc = now;
@@ -156,7 +159,8 @@  calc_latency(uint16_t pid __rte_unused,
 
 	now = rte_rdtsc();
 	for (i = 0; i < nb_pkts; i++) {
-		if (pkts[i]->timestamp)
+		if ((pkts[i]->ol_flags & PKT_RX_TIMESTAMP) &&
+				pkts[i]->timestamp)
 			latency[cnt++] = now - pkts[i]->timestamp;
 	}