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Message-ID: <CADEbmW2iX9BnUSh5vWY7tC6dtXX1-XJrY5Ox1K1JPjkemwBM9g@mail.gmail.com>
Date: Thu, 14 Mar 2024 19:49:49 +0100
From: Michal Schmidt <mschmidt@...hat.com>
To: Ivan Vecera <ivecera@...hat.com>
Cc: netdev@...r.kernel.org, pawel.chmielewski@...el.com,
aleksandr.loktionov@...el.com, Hugo Ferreira <hferreir@...hat.com>,
Jesse Brandeburg <jesse.brandeburg@...el.com>, Tony Nguyen <anthony.l.nguyen@...el.com>,
"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
Jacob Keller <jacob.e.keller@...el.com>,
"moderated list:INTEL ETHERNET DRIVERS" <intel-wired-lan@...ts.osuosl.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net v2] i40e: Enforce software interrupt during busy-poll exit
On Thu, Mar 14, 2024 at 1:00 PM Ivan Vecera <ivecera@...hat.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@...l-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@...l-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@...hat.com>
> Signed-off-by: Ivan Vecera <ivecera@...hat.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@...hat.com>
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