Subject: Re: [next-queue 3/3] i40e: Add i40e_napi_poll tracepoint

From: Maciej Fijalkowski <[email-masked]>
Date: Wed, 5 Oct 2022 12:27:30 +0200

On Wed, Oct 05, 2022 at 01:31:43AM -0700, Joe Damato wrote:

Hi Joe,

> Add a tracepoint for i40e_napi_poll that allows users to get detailed
> information about the amount of work done. This information can help users
> better tune the correct NAPI parameters (like weight and budget), as well
> as debug NIC settings like rx-usecs and tx-usecs, etc.
> 
> An example of the output from this tracepoint:
> 
> [...snip...]
> 
> 1029.268 :0/0 i40e:i40e_napi_poll(i40e_napi_poll on dev eth1 q
> i40e-eth1-TxRx-30 irq 172 irq_mask
> 00000000,00000000,00000000,00000010,00000000,00000000 curr_cpu 68 budget
> 64 bpr 64 work_done 0 tx_work_done 2 clean_complete 1 tx_clean_complete
> 1)
> 	i40e_napi_poll ([i40e])
> 	i40e_napi_poll ([i40e])
> 	__napi_poll ([kernel.kallsyms])
> 	net_rx_action ([kernel.kallsyms])
> 	__do_softirq ([kernel.kallsyms])
> 	common_interrupt ([kernel.kallsyms])
> 	asm_common_interrupt ([kernel.kallsyms])
> 	intel_idle_irq ([kernel.kallsyms])
> 	cpuidle_enter_state ([kernel.kallsyms])
> 	cpuidle_enter ([kernel.kallsyms])
> 	do_idle ([kernel.kallsyms])
> 	cpu_startup_entry ([kernel.kallsyms])
> 	[0x243fd8] ([kernel.kallsyms])
> 	secondary_startup_64_no_verify ([kernel.kallsyms])

maybe you could also include how to configure this tracepoint for future
readers?

> 
> Signed-off-by: Joe Damato <[email-masked]>
> ---
>  drivers/net/ethernet/intel/i40e/i40e_trace.h | 50 ++++++++++++++++++++++++++++
>  drivers/net/ethernet/intel/i40e/i40e_txrx.c  |  3 ++
>  2 files changed, 53 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_trace.h b/drivers/net/ethernet/intel/i40e/i40e_trace.h
> index b5b1229..779d046 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_trace.h
> +++ b/drivers/net/ethernet/intel/i40e/i40e_trace.h
> @@ -55,6 +55,56 @@
>   * being built from shared code.
>   */
>  
> +#define NO_DEV "(i40e no_device)"
> +
> +TRACE_EVENT(i40e_napi_poll,
> +
> +	TP_PROTO(struct napi_struct *napi, struct i40e_q_vector *q, int budget,
> +		 int budget_per_ring, int work_done, int tx_work_done, bool clean_complete,
> +		 bool tx_clean_complete),
> +
> +	TP_ARGS(napi, q, budget, budget_per_ring, work_done, tx_work_done,
> +		clean_complete, tx_clean_complete),
> +
> +	TP_STRUCT__entry(
> +		__field(int, budget)
> +		__field(int, budget_per_ring)
> +		__field(int, work_done)
> +		__field(int, tx_work_done)
> +		__field(int, clean_complete)
> +		__field(int, tx_clean_complete)
> +		__field(int, irq_num)
> +		__field(int, curr_cpu)
> +		__string(qname, q->name)
> +		__string(dev_name, napi->dev ? napi->dev->name : NO_DEV)
> +		__bitmask(irq_affinity,	nr_cpumask_bits)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->budget = budget;
> +		__entry->budget_per_ring = budget_per_ring;
> +		__entry->work_done = work_done;

What if rx clean routines failed to do allocation of new rx bufs? then
this would be misinterpreted. maybe we should change the API to

static bool
i40e_clean_rx_irq(struct i40e_ring *rx_ring, int budget,
		  unsigned int *processed_pkts);

so you would return failure and at the end do
	*processed_pkts = total_rx_packets;

then also i would change the naming of tracepoint entry. I'm not a native
english speaker but having 'done' within the variable name suggests to me
that it is rather a boolean. what about something like 'rx_cleaned_pkts'
instead?

Generally I think this is useful, personally I was in need of tracing the
next_to_clean and next_to_use ring indexes a lot, but that is probably out
of the scope in here.

> +		__entry->tx_work_done = tx_work_done;
> +		__entry->clean_complete = clean_complete;
> +		__entry->tx_clean_complete = tx_clean_complete;
> +		__entry->irq_num = q->irq_num;
> +		__entry->curr_cpu = get_cpu();
> +		__assign_str(qname, q->name);
> +		__assign_str(dev_name, napi->dev ? napi->dev->name : NO_DEV);
> +		__assign_bitmask(irq_affinity, cpumask_bits(&q->affinity_mask),
> +				 nr_cpumask_bits);
> +	),
> +
> +	TP_printk("i40e_napi_poll on dev %s q %s irq %d irq_mask %s curr_cpu %d "
> +		  "budget %d bpr %d work_done %d tx_work_done %d "
> +		  "clean_complete %d tx_clean_complete %d",
> +		__get_str(dev_name), __get_str(qname), __entry->irq_num,
> +		__get_bitmask(irq_affinity), __entry->curr_cpu, __entry->budget,
> +		__entry->budget_per_ring, __entry->work_done,
> +		__entry->tx_work_done,
> +		__entry->clean_complete, __entry->tx_clean_complete)
> +);
> +
>  /* Events related to a vsi & ring */
>  DECLARE_EVENT_CLASS(
>  	i40e_tx_template,
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> index ed88309..8b72f1b 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> @@ -2743,6 +2743,9 @@ int i40e_napi_poll(struct napi_struct *napi, int budget)
>  			clean_complete = false;
>  	}
>  
> +	trace_i40e_napi_poll(napi, q_vector, budget, budget_per_ring, work_done, tx_wd,
> +			     clean_complete, tx_clean_complete);
> +
>  	/* If work not completed, return budget and polling will return */
>  	if (!clean_complete || !tx_clean_complete) {
>  		int cpu_id = smp_processor_id();
> -- 
> 2.7.4
>