netdev - Re: [PATCH net-next 3/3] net: xilinx: axienet: Add statistics support

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Date: Fri, 14 Jun 2024 16:54:12 -0400
From: Sean Anderson <sean.anderson@...ux.dev>
To: Simon Horman <horms@...nel.org>
Cc: Radhey Shyam Pandey <radhey.shyam.pandey@....com>,
 netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 Michal Simek <michal.simek@....com>, Jakub Kicinski <kuba@...nel.org>,
 Russell King <linux@...linux.org.uk>, Paolo Abeni <pabeni@...hat.com>,
 Eric Dumazet <edumazet@...gle.com>, linux-kernel@...r.kernel.org,
 "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next 3/3] net: xilinx: axienet: Add statistics support

On 6/14/24 12:30, Simon Horman wrote:
> On Mon, Jun 10, 2024 at 07:10:22PM -0400, Sean Anderson wrote:
>> Add support for reading the statistics counters, if they are enabled.
>> The counters may be 64-bit, but we can't detect this as there's no
>> ability bit for it and the counters are read-only. Therefore, we assume
>> the counters are 32-bits. To ensure we don't miss an overflow, we need
>> to read all counters at regular intervals, configurable with
>> stats-block-usecs. This should be often enough to ensure the bytes
>> counters don't wrap at 2.5 Gbit/s.
>> 
>> Another complication is that the counters may be reset when the device
>> is reset (depending on configuration). To ensure the counters persist
>> across link up/down (including suspend/resume), we maintain our own
>> 64-bit versions along with the last counter value we saw. Because we
>> might wait up to 100 ms for the reset to complete, we use a mutex to
>> protect writing hw_stats. We can't sleep in ndo_get_stats64, so we use a
>> u64_stats_sync to protect readers.
>> 
>> We can't use the byte counters for either get_stats64 or
>> get_eth_mac_stats. This is because the byte counters include everything
>> in the frame (destination address to FCS, inclusive). But
>> rtnl_link_stats64 wants bytes excluding the FCS, and
>> ethtool_eth_mac_stats wants to exclude the L2 overhead (addresses and
>> length/type).
>> 
>> Signed-off-by: Sean Anderson <sean.anderson@...ux.dev>
>> ---
>> 
>>  drivers/net/ethernet/xilinx/xilinx_axienet.h  |  81 ++++++
>>  .../net/ethernet/xilinx/xilinx_axienet_main.c | 267 +++++++++++++++++-
>>  2 files changed, 345 insertions(+), 3 deletions(-)
>> 
>> diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet.h b/drivers/net/ethernet/xilinx/xilinx_axienet.h
> 
> ...
> 
>> @@ -434,6 +502,11 @@ struct skbuf_dma_descriptor {
>>   * @tx_packets: TX packet count for statistics
>>   * @tx_bytes:	TX byte count for statistics
>>   * @tx_stat_sync: Synchronization object for TX stats
>> + * @hw_last_counter: Last-seen value of each statistic
>> + * @hw_stats: Interface statistics periodically updated from hardware counters
>> + * @hw_stats_sync: Synchronization object for @hw_stats
> 
> nit: s/hw_stats_sync/hw_stat_sync/
> 
>      Flagged by kernel-doc -none

I think I will rename the member instead.

--Sean

>> + * @stats_lock: Lock for writing @hw_stats and @hw_last_counter
>> + * @stats_work: Work for reading the hardware statistics counters
>>   * @dma_err_task: Work structure to process Axi DMA errors
>>   * @tx_irq:	Axidma TX IRQ number
>>   * @rx_irq:	Axidma RX IRQ number
>> @@ -452,6 +525,7 @@ struct skbuf_dma_descriptor {
>>   * @coalesce_usec_rx:	IRQ coalesce delay for RX
>>   * @coalesce_count_tx:	Store the irq coalesce on TX side.
>>   * @coalesce_usec_tx:	IRQ coalesce delay for TX
>> + * @coalesce_usec_stats: Delay between hardware statistics refreshes
>>   * @use_dmaengine: flag to check dmaengine framework usage.
>>   * @tx_chan:	TX DMA channel.
>>   * @rx_chan:	RX DMA channel.
>> @@ -505,6 +579,12 @@ struct axienet_local {
>>  	u64_stats_t tx_bytes;
>>  	struct u64_stats_sync tx_stat_sync;
>>  
>> +	u32 hw_last_counter[STAT_COUNT];
>> +	u64_stats_t hw_stats[STAT_COUNT];
>> +	struct u64_stats_sync hw_stat_sync;
>> +	struct mutex stats_lock;
>> +	struct delayed_work stats_work;
>> +
>>  	struct work_struct dma_err_task;
>>  
>>  	int tx_irq;
> 
> ...