Message-ID: <CACT4oufpuQcV9Ma+3XwbiOGKev8Pq1Kk+f=QFX9KfURhjU-G=g@mail.gmail.com>
Date: Fri, 16 Jun 2023 09:10:30 +0200
From: Íñigo Huguet <ihuguet@...hat.com>
To: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Cc: ecree.xilinx@...il.com, habetsm.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 12:31 PM Maciej Fijalkowski
<maciej.fijalkowski@...el.com> wrote:
>
> 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.
>
> What is a v1..v2 diff? Please include this in future.

Oh, yes, sorry. I'm not inspired at all with this patch's
"administrative" requirements.

The only diff is the addition of the Fixes tags.

>
> >
> > 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!
>
> Hmm debug kernel is pretty wide term to me. maybe you could drop few
> config options specific to your setup?

I used RHEL's kernel-debug package. It has many debug options enabled,
but to name a few: kasan, lockdep, etc. In this case, I think that it
was mostly relevant to artificially increase the CPU stress in kernel
mode, nothing more.

>
> >
> > 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.
>
> please use imperative mood.
>
> >
> > 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>
> > ---
> >  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
> >
> >
>


-- 
Íñigo Huguet

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