[Intel-wired-lan] [PATCH net v2] i40e: Enforce software interrupt during busy-poll exit

Michal Schmidt mschmidt at redhat.com
Thu Mar 14 18:49:49 UTC 2024


On Thu, Mar 14, 2024 at 1:00 PM Ivan Vecera <ivecera at redhat.com> wrote:
>
> As for ice bug fixed by commit b7306b42beaf ("ice: manage interrupts
> during poll exit") followed by commit 23be7075b318 ("ice: fix software
> generating extra interrupts") I'm seeing the similar issue also with
> i40e driver.
>
> In certain situation when busy-loop is enabled together with adaptive
> coalescing, the driver occasionally misses that there are outstanding
> descriptors to clean when exiting busy poll.
>
> Try to catch the remaining work by triggering a software interrupt
> when exiting busy poll. No extra interrupts will be generated when
> busy polling is not used.
>
> The issue was found when running sockperf ping-pong tcp test with
> adaptive coalescing and busy poll enabled (50 as value busy_pool
> and busy_read sysctl knobs) and results in huge latency spikes
> with more than 100000us.
>
> The fix is inspired from the ice driver and do the following:
> 1) During napi poll exit in case of busy-poll (napo_complete_done()
>    returns false) this is recorded to q_vector that we were in busy
>    loop.
> 2) In i40e_update_enable_itr()
>    - updates refreshed ITR intervals directly using PFINT_ITRN register
>    - if we are exiting ordinary poll then just enables the interrupt
>      using PFINT_DYN_CTLN
>    - if we are exiting busy poll then enables the interrupt and
>      additionally triggers an immediate software interrupt to catch any
>      pending clean-ups
> 3) Reuses unused 3rd ITR (interrupt throttle) index and set it to
>    20K interrupts per second to limit the number of these sw interrupts.
>
> Test results
> ============
> Prior:
> [root at dell-per640-07 net]# sockperf ping-pong -i 10.9.9.1 --tcp -m 1000 --mps=max -t 120
> sockperf: == version #3.10-no.git ==
> sockperf[CLIENT] send on:sockperf: using recvfrom() to block on socket(s)
>
> [ 0] IP = 10.9.9.1        PORT = 11111 # TCP
> sockperf: Warmup stage (sending a few dummy messages)...
> sockperf: Starting test...
> sockperf: Test end (interrupted by timer)
> sockperf: Test ended
> sockperf: [Total Run] RunTime=119.999 sec; Warm up time=400 msec; SentMessages=2438563; ReceivedMessages=2438562
> sockperf: ========= Printing statistics for Server No: 0
> sockperf: [Valid Duration] RunTime=119.549 sec; SentMessages=2429473; ReceivedMessages=2429473
> sockperf: ====> avg-latency=24.571 (std-dev=93.297, mean-ad=4.904, median-ad=1.510, siqr=1.063, cv=3.797, std-error=0.060, 99.0% ci=[24.417, 24.725])
> sockperf: # dropped messages = 0; # duplicated messages = 0; # out-of-order messages = 0
> sockperf: Summary: Latency is 24.571 usec
> sockperf: Total 2429473 observations; each percentile contains 24294.73 observations
> sockperf: ---> <MAX> observation = 103294.331
> sockperf: ---> percentile 99.999 =   45.633
> sockperf: ---> percentile 99.990 =   37.013
> sockperf: ---> percentile 99.900 =   35.910
> sockperf: ---> percentile 99.000 =   33.390
> sockperf: ---> percentile 90.000 =   28.626
> sockperf: ---> percentile 75.000 =   27.741
> sockperf: ---> percentile 50.000 =   26.743
> sockperf: ---> percentile 25.000 =   25.614
> sockperf: ---> <MIN> observation =   12.220
>
> After:
> [root at dell-per640-07 net]# sockperf ping-pong -i 10.9.9.1 --tcp -m 1000 --mps=max -t 120
> sockperf: == version #3.10-no.git ==
> sockperf[CLIENT] send on:sockperf: using recvfrom() to block on socket(s)
>
> [ 0] IP = 10.9.9.1        PORT = 11111 # TCP
> sockperf: Warmup stage (sending a few dummy messages)...
> sockperf: Starting test...
> sockperf: Test end (interrupted by timer)
> sockperf: Test ended
> sockperf: [Total Run] RunTime=119.999 sec; Warm up time=400 msec; SentMessages=2400055; ReceivedMessages=2400054
> sockperf: ========= Printing statistics for Server No: 0
> sockperf: [Valid Duration] RunTime=119.549 sec; SentMessages=2391186; ReceivedMessages=2391186
> sockperf: ====> avg-latency=24.965 (std-dev=5.934, mean-ad=4.642, median-ad=1.485, siqr=1.067, cv=0.238, std-error=0.004, 99.0% ci=[24.955, 24.975])
> sockperf: # dropped messages = 0; # duplicated messages = 0; # out-of-order messages = 0
> sockperf: Summary: Latency is 24.965 usec
> sockperf: Total 2391186 observations; each percentile contains 23911.86 observations
> sockperf: ---> <MAX> observation =  195.841
> sockperf: ---> percentile 99.999 =   45.026
> sockperf: ---> percentile 99.990 =   39.009
> sockperf: ---> percentile 99.900 =   35.922
> sockperf: ---> percentile 99.000 =   33.482
> sockperf: ---> percentile 90.000 =   28.902
> sockperf: ---> percentile 75.000 =   27.821
> sockperf: ---> percentile 50.000 =   26.860
> sockperf: ---> percentile 25.000 =   25.685
> sockperf: ---> <MIN> observation =   12.277
>
> Fixes: 0bcd952feec7 ("ethernet/intel: consolidate NAPI and NAPI exit")
> Reported-by: Hugo Ferreira <hferreir at redhat.com>
> Signed-off-by: Ivan Vecera <ivecera at redhat.com>
> ---
>  drivers/net/ethernet/intel/i40e/i40e.h        |  1 +
>  drivers/net/ethernet/intel/i40e/i40e_main.c   |  6 +++
>  .../net/ethernet/intel/i40e/i40e_register.h   |  2 +
>  drivers/net/ethernet/intel/i40e/i40e_txrx.c   | 46 ++++++++++++++-----
>  drivers/net/ethernet/intel/i40e/i40e_txrx.h   |  1 +
>  5 files changed, 45 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/i40e/i40e.h b/drivers/net/ethernet/intel/i40e/i40e.h
> index ba24f3fa92c3..2fbabcdb5bb5 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e.h
> +++ b/drivers/net/ethernet/intel/i40e/i40e.h
> @@ -955,6 +955,7 @@ struct i40e_q_vector {
>         struct rcu_head rcu;    /* to avoid race with update stats on free */
>         char name[I40E_INT_NAME_STR_LEN];
>         bool arm_wb_state;
> +       bool in_busy_poll;
>         int irq_num;            /* IRQ assigned to this q_vector */
>  } ____cacheline_internodealigned_in_smp;
>
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c b/drivers/net/ethernet/intel/i40e/i40e_main.c
> index f86578857e8a..6576a0081093 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_main.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
> @@ -3911,6 +3911,12 @@ static void i40e_vsi_configure_msix(struct i40e_vsi *vsi)
>                      q_vector->tx.target_itr >> 1);
>                 q_vector->tx.current_itr = q_vector->tx.target_itr;
>
> +               /* Set ITR for software interrupts triggered after exiting
> +                * busy-loop polling.
> +                */
> +               wr32(hw, I40E_PFINT_ITRN(I40E_SW_ITR, vector - 1),
> +                    I40E_ITR_20K);
> +
>                 wr32(hw, I40E_PFINT_RATEN(vector - 1),
>                      i40e_intrl_usec_to_reg(vsi->int_rate_limit));
>
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_register.h b/drivers/net/ethernet/intel/i40e/i40e_register.h
> index 14ab642cafdb..baa6bb68bcf8 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_register.h
> +++ b/drivers/net/ethernet/intel/i40e/i40e_register.h
> @@ -335,6 +335,8 @@
>  #define I40E_PFINT_DYN_CTLN_INTERVAL_SHIFT 5
>  #define I40E_PFINT_DYN_CTLN_SW_ITR_INDX_ENA_SHIFT 24
>  #define I40E_PFINT_DYN_CTLN_SW_ITR_INDX_ENA_MASK I40E_MASK(0x1, I40E_PFINT_DYN_CTLN_SW_ITR_INDX_ENA_SHIFT)
> +#define I40E_PFINT_DYN_CTLN_SW_ITR_INDX_SHIFT 25
> +#define I40E_PFINT_DYN_CTLN_SW_ITR_INDX_MASK I40E_MASK(0x3, I40E_PFINT_DYN_CTLN_SW_ITR_INDX_SHIFT)
>  #define I40E_PFINT_ICR0 0x00038780 /* Reset: CORER */
>  #define I40E_PFINT_ICR0_INTEVENT_SHIFT 0
>  #define I40E_PFINT_ICR0_INTEVENT_MASK I40E_MASK(0x1, I40E_PFINT_ICR0_INTEVENT_SHIFT)
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> index 0d7177083708..356c3140adf3 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> @@ -2658,8 +2658,22 @@ static inline u32 i40e_buildreg_itr(const int type, u16 itr)
>         return val;
>  }
>
> -/* a small macro to shorten up some long lines */
> -#define INTREG I40E_PFINT_DYN_CTLN
> +static inline u32 i40e_buildreg_swint(int type)
> +{
> +       u32 val;
> +
> +       /* 1. Enable the interrupt
> +        * 2. Do not modify any ITR interval
> +        * 3. Trigger a SW interrupt specified by type
> +        */
> +       val = I40E_PFINT_DYN_CTLN_INTENA_MASK |
> +             I40E_PFINT_DYN_CTLN_ITR_INDX_MASK | /* set noitr */
> +             I40E_PFINT_DYN_CTLN_SWINT_TRIG_MASK |
> +             I40E_PFINT_DYN_CTLN_SW_ITR_INDX_ENA_MASK |
> +             FIELD_PREP(I40E_PFINT_DYN_CTLN_SW_ITR_INDX_MASK, type);
> +
> +       return val;
> +}
>
>  /* The act of updating the ITR will cause it to immediately trigger. In order
>   * to prevent this from throwing off adaptive update statistics we defer the
> @@ -2702,8 +2716,8 @@ static inline void i40e_update_enable_itr(struct i40e_vsi *vsi,
>          */
>         if (q_vector->rx.target_itr < q_vector->rx.current_itr) {
>                 /* Rx ITR needs to be reduced, this is highest priority */
> -               intval = i40e_buildreg_itr(I40E_RX_ITR,
> -                                          q_vector->rx.target_itr);
> +               wr32(hw, I40E_PFINT_ITRN(I40E_RX_ITR, q_vector->reg_idx),
> +                    q_vector->rx.target_itr >> 1);
>                 q_vector->rx.current_itr = q_vector->rx.target_itr;
>                 q_vector->itr_countdown = ITR_COUNTDOWN_START;
>         } else if ((q_vector->tx.target_itr < q_vector->tx.current_itr) ||
> @@ -2712,25 +2726,33 @@ static inline void i40e_update_enable_itr(struct i40e_vsi *vsi,
>                 /* Tx ITR needs to be reduced, this is second priority
>                  * Tx ITR needs to be increased more than Rx, fourth priority
>                  */
> -               intval = i40e_buildreg_itr(I40E_TX_ITR,
> -                                          q_vector->tx.target_itr);
> +               wr32(hw, I40E_PFINT_ITRN(I40E_TX_ITR, q_vector->reg_idx),
> +                    q_vector->tx.target_itr >> 1);
>                 q_vector->tx.current_itr = q_vector->tx.target_itr;
>                 q_vector->itr_countdown = ITR_COUNTDOWN_START;
>         } else if (q_vector->rx.current_itr != q_vector->rx.target_itr) {
>                 /* Rx ITR needs to be increased, third priority */
> -               intval = i40e_buildreg_itr(I40E_RX_ITR,
> -                                          q_vector->rx.target_itr);
> +               wr32(hw, I40E_PFINT_ITRN(I40E_RX_ITR, q_vector->reg_idx),
> +                    q_vector->rx.target_itr >> 1);
>                 q_vector->rx.current_itr = q_vector->rx.target_itr;
>                 q_vector->itr_countdown = ITR_COUNTDOWN_START;
>         } else {
>                 /* No ITR update, lowest priority */
> -               intval = i40e_buildreg_itr(I40E_ITR_NONE, 0);
>                 if (q_vector->itr_countdown)
>                         q_vector->itr_countdown--;
>         }
>
> -       if (!test_bit(__I40E_VSI_DOWN, vsi->state))
> -               wr32(hw, INTREG(q_vector->reg_idx), intval);
> +       /* Do not enable interrupt if VSI is down */
> +       if (test_bit(__I40E_VSI_DOWN, vsi->state))
> +               return;
> +
> +       if (!q_vector->in_busy_poll) {
> +               intval = i40e_buildreg_itr(I40E_ITR_NONE, 0);
> +       } else {
> +               q_vector->in_busy_poll = false;
> +               intval = i40e_buildreg_swint(I40E_SW_ITR);
> +       }
> +       wr32(hw, I40E_PFINT_DYN_CTLN(q_vector->reg_idx), intval);
>  }
>
>  /**
> @@ -2845,6 +2867,8 @@ int i40e_napi_poll(struct napi_struct *napi, int budget)
>          */
>         if (likely(napi_complete_done(napi, work_done)))
>                 i40e_update_enable_itr(vsi, q_vector);
> +       else
> +               q_vector->in_busy_poll = true;
>
>         return min(work_done, budget - 1);
>  }
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.h b/drivers/net/ethernet/intel/i40e/i40e_txrx.h
> index abf15067eb5d..2cdc7de6301c 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.h
> +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.h
> @@ -68,6 +68,7 @@ enum i40e_dyn_idx {
>  /* these are indexes into ITRN registers */
>  #define I40E_RX_ITR    I40E_IDX_ITR0
>  #define I40E_TX_ITR    I40E_IDX_ITR1
> +#define I40E_SW_ITR    I40E_IDX_ITR2
>
>  /* Supported RSS offloads */
>  #define I40E_DEFAULT_RSS_HENA ( \
> --
> 2.43.0

Reviewed-by: Michal Schmidt <mschmidt at redhat.com>



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