Subject: Re: [PATCH net] sfc: use budget for TX completions

From: Maciej Fijalkowski <[email-masked]>
Date: Mon, 12 Jun 2023 18:04:37 +0200

On Mon, Jun 12, 2023 at 04:42:54PM +0200, Íñigo Huguet wrote:

Hey Inigo, some trivial things below.

> When running workloads heavy unbalanced towards TX (high TX, low RX
> traffic), sfc driver can retain the CPU during too long times. Although
> in many cases this is not enough to be visible, it can affect
> performance and system responsiveness.
> 
> A way to reproduce it is to use a debug kernel and run some parallel
> netperf TX tests. In some systems, this will lead to this message being
> logged:
>   kernel:watchdog: BUG: soft lockup - CPU#12 stuck for 22s!
> 
> The reason is that sfc driver doesn't account any NAPI budget for the TX
> completion events work. With high-TX/low-RX traffic, this makes that the
> CPU is held for long time for NAPI poll.
> 
> Documentations says "drivers can process completions for any number of Tx
> packets but should only process up to budget number of Rx packets".
> However, many drivers do limit the amount of TX completions that they
> process in a single NAPI poll.
> 
> In the same way, this patch adds a limit for the TX work in sfc. With
> the patch applied, the watchdog warning never appears.
> 
> Tested with netperf in different combinations: single process / parallel
> processes, TCP / UDP and different sizes of UDP messages. Repeated the
> tests before and after the patch, without any noticeable difference in
> network or CPU performance.
> 
> Test hardware:
> Intel(R) Xeon(R) CPU E5-1620 v4 @ 3.50GHz (4 cores, 2 threads/core)
> Solarflare Communications XtremeScale X2522-25G Network Adapter
> 
> Reported-by: Fei Liu <[email-masked]>
> Signed-off-by: Íñigo Huguet <[email-masked]>

You're missing Fixes: tag.

> ---
>  drivers/net/ethernet/sfc/ef10.c      | 25 ++++++++++++++++++-------
>  drivers/net/ethernet/sfc/ef100_nic.c |  7 ++++++-
>  drivers/net/ethernet/sfc/ef100_tx.c  |  4 ++--
>  drivers/net/ethernet/sfc/ef100_tx.h  |  2 +-
>  drivers/net/ethernet/sfc/tx_common.c |  4 +++-
>  drivers/net/ethernet/sfc/tx_common.h |  2 +-
>  6 files changed, 31 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/net/ethernet/sfc/ef10.c b/drivers/net/ethernet/sfc/ef10.c
> index d30459dbfe8f..b63e47af6365 100644
> --- a/drivers/net/ethernet/sfc/ef10.c
> +++ b/drivers/net/ethernet/sfc/ef10.c
> @@ -2950,7 +2950,7 @@ static u32 efx_ef10_extract_event_ts(efx_qword_t *event)
>  	return tstamp;
>  }
>  
> -static void
> +static int
>  efx_ef10_handle_tx_event(struct efx_channel *channel, efx_qword_t *event)
>  {
>  	struct efx_nic *efx = channel->efx;
> @@ -2958,13 +2958,14 @@ efx_ef10_handle_tx_event(struct efx_channel *channel, efx_qword_t *event)
>  	unsigned int tx_ev_desc_ptr;
>  	unsigned int tx_ev_q_label;
>  	unsigned int tx_ev_type;
> +	int work_done;
>  	u64 ts_part;
>  
>  	if (unlikely(READ_ONCE(efx->reset_pending)))
> -		return;
> +		return 0;
>  
>  	if (unlikely(EFX_QWORD_FIELD(*event, ESF_DZ_TX_DROP_EVENT)))
> -		return;
> +		return 0;
>  
>  	/* Get the transmit queue */
>  	tx_ev_q_label = EFX_QWORD_FIELD(*event, ESF_DZ_TX_QLABEL);
> @@ -2973,8 +2974,7 @@ efx_ef10_handle_tx_event(struct efx_channel *channel, efx_qword_t *event)
>  	if (!tx_queue->timestamping) {
>  		/* Transmit completion */
>  		tx_ev_desc_ptr = EFX_QWORD_FIELD(*event, ESF_DZ_TX_DESCR_INDX);
> -		efx_xmit_done(tx_queue, tx_ev_desc_ptr & tx_queue->ptr_mask);
> -		return;
> +		return efx_xmit_done(tx_queue, tx_ev_desc_ptr & tx_queue->ptr_mask);
>  	}
>  
>  	/* Transmit timestamps are only available for 8XXX series. They result
> @@ -3000,6 +3000,7 @@ efx_ef10_handle_tx_event(struct efx_channel *channel, efx_qword_t *event)
>  	 * fields in the event.
>  	 */
>  	tx_ev_type = EFX_QWORD_FIELD(*event, ESF_EZ_TX_SOFT1);
> +	work_done = 0;
>  
>  	switch (tx_ev_type) {
>  	case TX_TIMESTAMP_EVENT_TX_EV_COMPLETION:
> @@ -3016,6 +3017,7 @@ efx_ef10_handle_tx_event(struct efx_channel *channel, efx_qword_t *event)
>  		tx_queue->completed_timestamp_major = ts_part;
>  
>  		efx_xmit_done_single(tx_queue);
> +		work_done = 1;
>  		break;
>  
>  	default:
> @@ -3026,6 +3028,8 @@ efx_ef10_handle_tx_event(struct efx_channel *channel, efx_qword_t *event)
>  			  EFX_QWORD_VAL(*event));
>  		break;
>  	}
> +
> +	return work_done;
>  }
>  
>  static void
> @@ -3081,13 +3085,16 @@ static void efx_ef10_handle_driver_generated_event(struct efx_channel *channel,
>  	}
>  }
>  
> +#define EFX_NAPI_MAX_TX 512
> +
>  static int efx_ef10_ev_process(struct efx_channel *channel, int quota)
>  {
>  	struct efx_nic *efx = channel->efx;
>  	efx_qword_t event, *p_event;
>  	unsigned int read_ptr;
> -	int ev_code;
> +	int spent_tx = 0;
>  	int spent = 0;
> +	int ev_code;
>  
>  	if (quota <= 0)
>  		return spent;
> @@ -3126,7 +3133,11 @@ static int efx_ef10_ev_process(struct efx_channel *channel, int quota)
>  			}
>  			break;
>  		case ESE_DZ_EV_CODE_TX_EV:
> -			efx_ef10_handle_tx_event(channel, &event);
> +			spent_tx += efx_ef10_handle_tx_event(channel, &event);
> +			if (spent_tx >= EFX_NAPI_MAX_TX) {
> +				spent = quota;
> +				goto out;
> +			}
>  			break;
>  		case ESE_DZ_EV_CODE_DRIVER_EV:
>  			efx_ef10_handle_driver_event(channel, &event);
> diff --git a/drivers/net/ethernet/sfc/ef100_nic.c b/drivers/net/ethernet/sfc/ef100_nic.c
> index 4dc643b0d2db..7adde9639c8a 100644
> --- a/drivers/net/ethernet/sfc/ef100_nic.c
> +++ b/drivers/net/ethernet/sfc/ef100_nic.c
> @@ -253,6 +253,8 @@ static void ef100_ev_read_ack(struct efx_channel *channel)
>  		   efx_reg(channel->efx, ER_GZ_EVQ_INT_PRIME));
>  }
>  
> +#define EFX_NAPI_MAX_TX 512

couldn't this go to tx_common.h ? you're defining this two times.

> +
>  static int ef100_ev_process(struct efx_channel *channel, int quota)
>  {
>  	struct efx_nic *efx = channel->efx;
> @@ -260,6 +262,7 @@ static int ef100_ev_process(struct efx_channel *channel, int quota)
>  	bool evq_phase, old_evq_phase;
>  	unsigned int read_ptr;
>  	efx_qword_t *p_event;
> +	int spent_tx = 0;
>  	int spent = 0;
>  	bool ev_phase;
>  	int ev_type;
> @@ -295,7 +298,9 @@ static int ef100_ev_process(struct efx_channel *channel, int quota)
>  			efx_mcdi_process_event(channel, p_event);
>  			break;
>  		case ESE_GZ_EF100_EV_TX_COMPLETION:
> -			ef100_ev_tx(channel, p_event);
> +			spent_tx += ef100_ev_tx(channel, p_event);
> +			if (spent_tx >= EFX_NAPI_MAX_TX)
> +				spent = quota;
>  			break;
>  		case ESE_GZ_EF100_EV_DRIVER:
>  			netif_info(efx, drv, efx->net_dev,
> diff --git a/drivers/net/ethernet/sfc/ef100_tx.c b/drivers/net/ethernet/sfc/ef100_tx.c
> index 29ffaf35559d..849e5555bd12 100644
> --- a/drivers/net/ethernet/sfc/ef100_tx.c
> +++ b/drivers/net/ethernet/sfc/ef100_tx.c
> @@ -346,7 +346,7 @@ void ef100_tx_write(struct efx_tx_queue *tx_queue)
>  	ef100_tx_push_buffers(tx_queue);
>  }
>  
> -void ef100_ev_tx(struct efx_channel *channel, const efx_qword_t *p_event)
> +int ef100_ev_tx(struct efx_channel *channel, const efx_qword_t *p_event)
>  {
>  	unsigned int tx_done =
>  		EFX_QWORD_FIELD(*p_event, ESF_GZ_EV_TXCMPL_NUM_DESC);
> @@ -357,7 +357,7 @@ void ef100_ev_tx(struct efx_channel *channel, const efx_qword_t *p_event)
>  	unsigned int tx_index = (tx_queue->read_count + tx_done - 1) &
>  				tx_queue->ptr_mask;
>  
> -	efx_xmit_done(tx_queue, tx_index);
> +	return efx_xmit_done(tx_queue, tx_index);
>  }
>  
>  /* Add a socket buffer to a TX queue
> diff --git a/drivers/net/ethernet/sfc/ef100_tx.h b/drivers/net/ethernet/sfc/ef100_tx.h
> index e9e11540fcde..d9a0819c5a72 100644
> --- a/drivers/net/ethernet/sfc/ef100_tx.h
> +++ b/drivers/net/ethernet/sfc/ef100_tx.h
> @@ -20,7 +20,7 @@ void ef100_tx_init(struct efx_tx_queue *tx_queue);
>  void ef100_tx_write(struct efx_tx_queue *tx_queue);
>  unsigned int ef100_tx_max_skb_descs(struct efx_nic *efx);
>  
> -void ef100_ev_tx(struct efx_channel *channel, const efx_qword_t *p_event);
> +int ef100_ev_tx(struct efx_channel *channel, const efx_qword_t *p_event);
>  
>  netdev_tx_t ef100_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb);
>  int __ef100_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb,
> diff --git a/drivers/net/ethernet/sfc/tx_common.c b/drivers/net/ethernet/sfc/tx_common.c
> index 67e789b96c43..755aa92bf823 100644
> --- a/drivers/net/ethernet/sfc/tx_common.c
> +++ b/drivers/net/ethernet/sfc/tx_common.c
> @@ -249,7 +249,7 @@ void efx_xmit_done_check_empty(struct efx_tx_queue *tx_queue)
>  	}
>  }
>  
> -void efx_xmit_done(struct efx_tx_queue *tx_queue, unsigned int index)
> +int efx_xmit_done(struct efx_tx_queue *tx_queue, unsigned int index)
>  {
>  	unsigned int fill_level, pkts_compl = 0, bytes_compl = 0;
>  	unsigned int efv_pkts_compl = 0;
> @@ -279,6 +279,8 @@ void efx_xmit_done(struct efx_tx_queue *tx_queue, unsigned int index)
>  	}
>  
>  	efx_xmit_done_check_empty(tx_queue);
> +
> +	return pkts_compl + efv_pkts_compl;
>  }
>  
>  /* Remove buffers put into a tx_queue for the current packet.
> diff --git a/drivers/net/ethernet/sfc/tx_common.h b/drivers/net/ethernet/sfc/tx_common.h
> index d87aecbc7bf1..1e9f42938aac 100644
> --- a/drivers/net/ethernet/sfc/tx_common.h
> +++ b/drivers/net/ethernet/sfc/tx_common.h
> @@ -28,7 +28,7 @@ static inline bool efx_tx_buffer_in_use(struct efx_tx_buffer *buffer)
>  }
>  
>  void efx_xmit_done_check_empty(struct efx_tx_queue *tx_queue);
> -void efx_xmit_done(struct efx_tx_queue *tx_queue, unsigned int index);
> +int efx_xmit_done(struct efx_tx_queue *tx_queue, unsigned int index);
>  
>  void efx_enqueue_unwind(struct efx_tx_queue *tx_queue,
>  			unsigned int insert_count);
> -- 
> 2.40.1
> 
>