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Message-ID: <ZIwULFLDmZKLkRuP@gmail.com>
Date: Fri, 16 Jun 2023 08:50:04 +0100
From: Martin Habets <habetsm.xilinx@...il.com>
To: Íñigo Huguet <ihuguet@...hat.com>
Cc: ecree.xilinx@...il.com, davem@...emloft.net, edumazet@...gle.com,
kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org,
linux-net-drivers@....com, bkenward@...arflare.com,
Fei Liu <feliu@...hat.com>
Subject: Re: [PATCH v2 net] sfc: use budget for TX completions
On Thu, Jun 15, 2023 at 10:49:29AM +0200, Íñigo Huguet wrote:
> 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
>
> Fixes: 5227ecccea2d ("sfc: remove tx and MCDI handling from NAPI budget consideration")
> Fixes: d19a53721863 ("sfc_ef100: TX path for EF100 NICs")
> Reported-by: Fei Liu <feliu@...hat.com>
> Signed-off-by: Íñigo Huguet <ihuguet@...hat.com>
Acked-by: Martin Habets <habetsm.xilinx@...il.com>
> ---
> 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
> +
> 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
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