Re: [PATCH net v4] i40e: Enforce software interrupt during busy-poll exit

From: Jesse Brandeburg
Date: Tue Mar 19 2024 - 13:45:00 EST

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In reply to: Michal Schmidt: "Re: [PATCH net v4] i40e: Enforce software interrupt during busy-poll exit"
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On 3/16/2024 4:38 AM, Ivan Vecera 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) Extends i40e_buildreg_itr() to be able to add an enforced software
> interrupt into built value
> 2) In i40e_update_enable_itr() enforces a software interrupt trigger
> if we are exiting busy poll 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@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@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@xxxxxxxxxx>
> Reviewed-by: Michal Schmidt <mschmidt@xxxxxxxxxx>
> Signed-off-by: Ivan Vecera <ivecera@xxxxxxxxxx>

Thank you!

Reviewed-by: Jesse Brandeburg <jesse.brandeburg@xxxxxxxxx>

> ---
> Changes since v3
> - fixed kdoc warnings (thx Tony)
> Changes since v2
> - eliminated two writes in hot-path (thx Jesse)
> Changes since v1
> - added Fixes: tag
>
> drivers/net/ethernet/intel/i40e/i40e.h | 1 +
> drivers/net/ethernet/intel/i40e/i40e_main.c | 6 ++
> .../net/ethernet/intel/i40e/i40e_register.h | 3 +
> drivers/net/ethernet/intel/i40e/i40e_txrx.c | 82 ++++++++++++++-----
> drivers/net/ethernet/intel/i40e/i40e_txrx.h | 1 +
> 5 files changed, 72 insertions(+), 21 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 83c020ae9625..70ead95af2c1 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_main.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
> @@ -3922,6 +3922,12 @@ 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..432afbb64201 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_register.h
> +++ b/drivers/net/ethernet/intel/i40e/i40e_register.h
> @@ -333,8 +333,11 @@
> #define I40E_PFINT_DYN_CTLN_ITR_INDX_SHIFT 3
> #define I40E_PFINT_DYN_CTLN_ITR_INDX_MASK I40E_MASK(0x3, I40E_PFINT_DYN_CTLN_ITR_INDX_SHIFT)
> #define I40E_PFINT_DYN_CTLN_INTERVAL_SHIFT 5
> +#define I40E_PFINT_DYN_CTLN_INTERVAL_MASK I40E_MASK(0xFFF, I40E_PFINT_DYN_CTLN_INTERVAL_SHIFT)
> #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..1a12b732818e 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> @@ -2630,7 +2630,22 @@ static int i40e_clean_rx_irq(struct i40e_ring *rx_ring, int budget,
> return failure ? budget : (int)total_rx_packets;
> }
>
> -static inline u32 i40e_buildreg_itr(const int type, u16 itr)
> +/**
> + * i40e_buildreg_itr - build a value for writing to I40E_PFINT_DYN_CTLN register
> + * @itr_idx: interrupt throttling index
> + * @interval: interrupt throttling interval value in usecs
> + * @force_swint: force software interrupt
> + *
> + * The function builds a value for I40E_PFINT_DYN_CTLN register that
> + * is used to update interrupt throttling interval for specified ITR index
> + * and optionally enforces a software interrupt. If the @itr_idx is equal
> + * to I40E_ITR_NONE then no interval change is applied and only @force_swint
> + * parameter is taken into account. If the interval change and enforced
> + * software interrupt are not requested then the built value just enables
> + * appropriate vector interrupt.
> + **/

Thanks for adding the kdoc!

> +static u32 i40e_buildreg_itr(enum i40e_dyn_idx itr_idx, u16 interval,
> + bool force_swint)
> {
> u32 val;
>
> @@ -2644,23 +2659,33 @@ static inline u32 i40e_buildreg_itr(const int type, u16 itr)
> * an event in the PBA anyway so we need to rely on the automask
> * to hold pending events for us until the interrupt is re-enabled
> *
> - * The itr value is reported in microseconds, and the register
> - * value is recorded in 2 microsecond units. For this reason we
> - * only need to shift by the interval shift - 1 instead of the
> - * full value.
> + * We have to shift the given value as it is reported in microseconds
> + * and the register value is recorded in 2 microsecond units.
> */
> - itr &= I40E_ITR_MASK;
> + interval >>= 1;
>
> + /* 1. Enable vector interrupt
> + * 2. Update the interval for the specified ITR index
> + * (I40E_ITR_NONE in the register is used to indicate that
> + * no interval update is requested)
> + */
> val = I40E_PFINT_DYN_CTLN_INTENA_MASK |
> - (type << I40E_PFINT_DYN_CTLN_ITR_INDX_SHIFT) |
> - (itr << (I40E_PFINT_DYN_CTLN_INTERVAL_SHIFT - 1));
> + FIELD_PREP(I40E_PFINT_DYN_CTLN_ITR_INDX_MASK, itr_idx) |
> + FIELD_PREP(I40E_PFINT_DYN_CTLN_INTERVAL_MASK, interval);
> +
> + /* 3. Enforce software interrupt trigger if requested
> + * (These software interrupts rate is limited by ITR2 that is
> + * set to 20K interrupts per second)
> + */
> + if (force_swint)
> + val |= 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,
> + I40E_SW_ITR);
>
> return val;
> }
>
> -/* a small macro to shorten up some long lines */
> -#define INTREG I40E_PFINT_DYN_CTLN
> -
> /* 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
> * update so that it can only happen so often. So after either Tx or Rx are
> @@ -2679,8 +2704,10 @@ static inline u32 i40e_buildreg_itr(const int type, u16 itr)
> static inline void i40e_update_enable_itr(struct i40e_vsi *vsi,
> struct i40e_q_vector *q_vector)
> {
> + enum i40e_dyn_idx itr_idx = I40E_ITR_NONE;
> struct i40e_hw *hw = &vsi->back->hw;
> - u32 intval;
> + u16 interval = 0;
> + u32 itr_val;
>
> /* If we don't have MSIX, then we only need to re-enable icr0 */
> if (!test_bit(I40E_FLAG_MSIX_ENA, vsi->back->flags)) {
> @@ -2702,8 +2729,8 @@ 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);
> + itr_idx = I40E_RX_ITR;
> + interval = q_vector->rx.target_itr;
> 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 +2739,36 @@ 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);
> + itr_idx = I40E_TX_ITR;
> + interval = q_vector->tx.target_itr;
> 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);
> + itr_idx = I40E_RX_ITR;
> + interval = q_vector->rx.target_itr;
> 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 update interrupt control register if VSI is down */
> + if (test_bit(__I40E_VSI_DOWN, vsi->state))
> + return;
> +
> + /* Update ITR interval if necessary and enforce software interrupt
> + * if we are exiting busy poll.
> + */
> + if (q_vector->in_busy_poll) {
> + itr_val = i40e_buildreg_itr(itr_idx, interval, true);
> + q_vector->in_busy_poll = false;
> + } else {
> + itr_val = i40e_buildreg_itr(itr_idx, interval, false);
> + }
> + wr32(hw, I40E_PFINT_DYN_CTLN(q_vector->reg_idx), itr_val);
> }
>
> /**
> @@ -2845,6 +2883,8 @@ 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 ( \

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