[PATCH] net/mlx5e: Report rx_discards_phy via rx_missed_errors

[PATCH] net/mlx5e: Report rx_discards_phy via rx_missed_errors

[Yafang Shao]

We observed a high number of rx_discards_phy events on some servers when
running `ethtool -S`. However, this important counter is not currently
reflected in the /proc/net/dev statistics file, making it challenging to
monitor effectively.

Since rx_missed_errors represents packets dropped due to buffer exhaustion,
it makes sense to include rx_discards_phy in this counter to enhance
monitoring visibility. This change will help administrators track these
events more effectively through standard interfaces.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Cc: Saeed Mahameed <saeedm@nvidia.com>
Cc: Tariq Toukan <tariqt@nvidia.com>
Cc: Leon Romanovsky <leon@kernel.org>
---
 drivers/net/ethernet/mellanox/mlx5/core/en_main.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
index 6f686fabed44..42c1b791a74c 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
@@ -3903,7 +3903,8 @@ mlx5e_get_stats(struct net_device *dev, struct rtnl_link_stats64 *stats)
 		mlx5e_fold_sw_stats64(priv, stats);
 	}
 
-	stats->rx_missed_errors = priv->stats.qcnt.rx_out_of_buffer;
+	stats->rx_missed_errors = priv->stats.qcnt.rx_out_of_buffer +
+				  PPORT_2863_GET(pstats, if_in_discards);
 
 	stats->rx_length_errors =
 		PPORT_802_3_GET(pstats, a_in_range_length_errors) +
-- 
2.30.1 (Apple Git-130)

Re: [PATCH] net/mlx5e: Report rx_discards_phy via rx_missed_errors

[Tariq Toukan]

On 06/11/2024 8:40, Yafang Shao wrote:
> We observed a high number of rx_discards_phy events on some servers when
> running `ethtool -S`. However, this important counter is not currently
> reflected in the /proc/net/dev statistics file, making it challenging to
> monitor effectively.
> 
> Since rx_missed_errors represents packets dropped due to buffer exhaustion,
> it makes sense to include rx_discards_phy in this counter to enhance
> monitoring visibility. This change will help administrators track these
> events more effectively through standard interfaces.
> 

Hi,

Thanks for your patch.

It's a matter of interpretation...
The documentation in 
Documentation/ABI/testing/sysfs-class-net-statistics refers to the 
driver for the exact meaning.

rx_discards_phy counts packet drops due to exhaustion of the physical 
port memory (not in the host), this happen way before steering the 
packet to any receive queue.
Today, rx_missed_errors counts SW/host memory buffer exhaustion of the 
receive queues.
I don't think that rx_missed_errors should mix both.

Maybe some other counter can be used for rx_discards_phy, like 
rx_fifo_errors?


> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> Cc: Saeed Mahameed <saeedm@nvidia.com>
> Cc: Tariq Toukan <tariqt@nvidia.com>
> Cc: Leon Romanovsky <leon@kernel.org>
> ---
>   drivers/net/ethernet/mellanox/mlx5/core/en_main.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> index 6f686fabed44..42c1b791a74c 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> @@ -3903,7 +3903,8 @@ mlx5e_get_stats(struct net_device *dev, struct rtnl_link_stats64 *stats)
>   		mlx5e_fold_sw_stats64(priv, stats);
>   	}
>   
> -	stats->rx_missed_errors = priv->stats.qcnt.rx_out_of_buffer;
> +	stats->rx_missed_errors = priv->stats.qcnt.rx_out_of_buffer +
> +				  PPORT_2863_GET(pstats, if_in_discards);
>   
>   	stats->rx_length_errors =
>   		PPORT_802_3_GET(pstats, a_in_range_length_errors) +

Re: [PATCH] net/mlx5e: Report rx_discards_phy via rx_missed_errors

[Yafang Shao]

On Wed, Nov 6, 2024 at 5:56 PM Tariq Toukan <ttoukan.linux@gmail.com> wrote:
>
>
>
> On 06/11/2024 8:40, Yafang Shao wrote:
> > We observed a high number of rx_discards_phy events on some servers when
> > running `ethtool -S`. However, this important counter is not currently
> > reflected in the /proc/net/dev statistics file, making it challenging to
> > monitor effectively.
> >
> > Since rx_missed_errors represents packets dropped due to buffer exhaustion,
> > it makes sense to include rx_discards_phy in this counter to enhance
> > monitoring visibility. This change will help administrators track these
> > events more effectively through standard interfaces.
> >
>
> Hi,
>
> Thanks for your patch.
>
> It's a matter of interpretation...
> The documentation in
> Documentation/ABI/testing/sysfs-class-net-statistics refers to the
> driver for the exact meaning.
>
> rx_discards_phy counts packet drops due to exhaustion of the physical
> port memory (not in the host), this happen way before steering the
> packet to any receive queue.
> Today, rx_missed_errors counts SW/host memory buffer exhaustion of the
> receive queues.
> I don't think that rx_missed_errors should mix both.

Thanks for your detailed explanation.

>
> Maybe some other counter can be used for rx_discards_phy, like
> rx_fifo_errors?

It appears that rx_fifo_errors is a more appropriate counter for this purpose.
I will submit a v2. Thanks for your suggestion.

-- 
Regards
Yafang

Re: [PATCH] net/mlx5e: Report rx_discards_phy via rx_missed_errors

[Gal Pressman]

On 06/11/2024 13:49, Yafang Shao wrote:
> On Wed, Nov 6, 2024 at 5:56 PM Tariq Toukan <ttoukan.linux@gmail.com> wrote:
>>
>>
>>
>> On 06/11/2024 8:40, Yafang Shao wrote:
>>> We observed a high number of rx_discards_phy events on some servers when
>>> running `ethtool -S`. However, this important counter is not currently
>>> reflected in the /proc/net/dev statistics file, making it challenging to
>>> monitor effectively.
>>>
>>> Since rx_missed_errors represents packets dropped due to buffer exhaustion,
>>> it makes sense to include rx_discards_phy in this counter to enhance
>>> monitoring visibility. This change will help administrators track these
>>> events more effectively through standard interfaces.
>>>
>>
>> Hi,
>>
>> Thanks for your patch.
>>
>> It's a matter of interpretation...
>> The documentation in
>> Documentation/ABI/testing/sysfs-class-net-statistics refers to the
>> driver for the exact meaning.

I think this documentation is outdated, a more recent one is in if_link.h:

 * @rx_missed_errors: Count of packets missed by the host.
 *   Folded into the "drop" counter in `/proc/net/dev`.
 *
 *   Counts number of packets dropped by the device due to lack
 *   of buffer space. This usually indicates that the host interface
 *   is slower than the network interface, or host is not keeping up
 *   with the receive packet rate.
 *
 *   This statistic corresponds to hardware events and is not used
 *   on software devices.

>>
>> rx_discards_phy counts packet drops due to exhaustion of the physical
>> port memory (not in the host), this happen way before steering the
>> packet to any receive queue.
>> Today, rx_missed_errors counts SW/host memory buffer exhaustion of the
>> receive queues.
>> I don't think that rx_missed_errors should mix both.
> 
> Thanks for your detailed explanation.
> 
>>
>> Maybe some other counter can be used for rx_discards_phy, like
>> rx_fifo_errors?
> 
> It appears that rx_fifo_errors is a more appropriate counter for this purpose.
> I will submit a v2. Thanks for your suggestion.

Probably not a good idea:
 *   This statistics was used interchangeably with @rx_over_errors.
 *   Not recommended for use in drivers for high speed interfaces.

Re: [PATCH] net/mlx5e: Report rx_discards_phy via rx_missed_errors

[Jakub Kicinski]

On Wed, 6 Nov 2024 21:23:47 +0200 Gal Pressman wrote:
> > It appears that rx_fifo_errors is a more appropriate counter for this purpose.
> > I will submit a v2. Thanks for your suggestion.  
> 
> Probably not a good idea:
>  *   This statistics was used interchangeably with @rx_over_errors.
>  *   Not recommended for use in drivers for high speed interfaces.

FWIW we can change the definition. Let me copy paste below the commit
which added the docs because it has the background.

tl;dr is that I was trying to push drivers towards a single stat to
keep things simple. If we have a clear definition of how rx_fifo_errors
would differ - we can reuse it and update the doc. For example if
rx_discards_phy usually means that the adapter itself is overwhelmed
(too many rules etc) that would be a pretty clear, since rx_missed is
supposed to primarily indicate that the host rings are full or perhaps
the PCIe interface of the NIC is struggling. But not the packet
processing.



commit 0db0c34cfbc9838c1a14cb04dd880602abd699a7
Author: Jakub Kicinski <kuba@kernel.org>
Date:   Thu Sep 3 16:14:31 2020 -0700

    net: tighten the definition of interface statistics
    
    This patch is born out of an investigation into which IEEE statistics
    correspond to which struct rtnl_link_stats64 members. Turns out that
    there seems to be reasonable consensus on the matter, among many drivers.
    To save others the time (and it took more time than I'm comfortable
    admitting) I'm adding comments referring to IEEE attributes to
    struct rtnl_link_stats64.
    
    Up until now we had two forms of documentation for stats - in
    Documentation/ABI/testing/sysfs-class-net-statistics and the comments
    on struct rtnl_link_stats64 itself. While the former is very cautious
    in defining the expected behavior, the latter feel quite dated and
    may not be easy to understand for modern day driver author
    (e.g. rx_over_errors). At the same time modern systems are far more
    complex and once obvious definitions lost their clarity. For example
    - does rx_packet count at the MAC layer (aFramesReceivedOK)?
    packets processed correctly by hardware? received by the driver?
    or maybe received by the stack?
    
    I tried to clarify the expectations, further clarifications from
    others are very welcome.
    
    The part hardest to untangle is rx_over_errors vs rx_fifo_errors
    vs rx_missed_errors. After much deliberation I concluded that for
    modern HW only two of the counters will make sense. The distinction
    between internal FIFO overflow and packets dropped due to back-pressure
    from the host is likely too implementation (driver and device) specific
    to expose in the standard stats.
    
    Now - which two of those counters we select to use is anyone's pick:
    
    sysfs documentation suggests rx_over_errors counts packets which
    did not fit into buffers due to MTU being too small, which I reused.
    There don't seem to be many modern drivers using it (well, CAN drivers
    seem to love this statistic).
    
    Of the remaining two I picked rx_missed_errors to report device drops.
    bnxt reports it and it's folded into "drop"s in procfs (while
    rx_fifo_errors is an error, and modern devices usually receive the frame
    OK, they just can't admit it into the pipeline).
    
    Of the drivers I looked at only AMD Lance-like and NS8390-like use all
    three of these counters. rx_missed_errors counts missed frames,
    rx_over_errors counts overflow events, and rx_fifo_errors counts frames
    which were truncated because they didn't fit into buffers. This suggests
    that rx_fifo_errors may be the correct stat for truncated packets, but
    I'd think a FIFO stat counting truncated packets would be very confusing
    to a modern reader.

Re: [PATCH] net/mlx5e: Report rx_discards_phy via rx_missed_errors

[Yafang Shao]

On Thu, Nov 7, 2024 at 9:17 AM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Wed, 6 Nov 2024 21:23:47 +0200 Gal Pressman wrote:
> > > It appears that rx_fifo_errors is a more appropriate counter for this purpose.
> > > I will submit a v2. Thanks for your suggestion.
> >
> > Probably not a good idea:
> >  *   This statistics was used interchangeably with @rx_over_errors.
> >  *   Not recommended for use in drivers for high speed interfaces.
>
> FWIW we can change the definition. Let me copy paste below the commit
> which added the docs because it has the background.
>
> tl;dr is that I was trying to push drivers towards a single stat to
> keep things simple. If we have a clear definition of how rx_fifo_errors
> would differ - we can reuse it and update the doc. For example if
> rx_discards_phy usually means that the adapter itself is overwhelmed
> (too many rules etc) that would be a pretty clear, since rx_missed is
> supposed to primarily indicate that the host rings are full or perhaps
> the PCIe interface of the NIC is struggling. But not the packet
> processing.

Thanks for providing the background.
What do you suggest—should we report rx_discards_phy via
rx_fifo_errors and update the documentation accordingly?

-- 
Regards
Yafang

Re: [PATCH] net/mlx5e: Report rx_discards_phy via rx_missed_errors

[Yafang Shao]

On Thu, Nov 7, 2024 at 3:23 AM Gal Pressman <gal@nvidia.com> wrote:
>
> On 06/11/2024 13:49, Yafang Shao wrote:
> > On Wed, Nov 6, 2024 at 5:56 PM Tariq Toukan <ttoukan.linux@gmail.com> wrote:
> >>
> >>
> >>
> >> On 06/11/2024 8:40, Yafang Shao wrote:
> >>> We observed a high number of rx_discards_phy events on some servers when
> >>> running `ethtool -S`. However, this important counter is not currently
> >>> reflected in the /proc/net/dev statistics file, making it challenging to
> >>> monitor effectively.
> >>>
> >>> Since rx_missed_errors represents packets dropped due to buffer exhaustion,
> >>> it makes sense to include rx_discards_phy in this counter to enhance
> >>> monitoring visibility. This change will help administrators track these
> >>> events more effectively through standard interfaces.
> >>>
> >>
> >> Hi,
> >>
> >> Thanks for your patch.
> >>
> >> It's a matter of interpretation...
> >> The documentation in
> >> Documentation/ABI/testing/sysfs-class-net-statistics refers to the
> >> driver for the exact meaning.
>
> I think this documentation is outdated, a more recent one is in if_link.h:

Should we sync the documentation in if_link.h with
Documentation/ABI/testing/sysfs-class-net-statistics?

-- 
Regards
Yafang