Date:   Mon, 17 Jun 2019 16:49:04 +0000
From:   Manish Chopra <manishc@...vell.com>
To:     Benjamin Poirier <bpoirier@...e.com>,
        GR-Linux-NIC-Dev <GR-Linux-NIC-Dev@...vell.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH net-next 01/16] qlge: Remove irq_cnt

> -----Original Message-----
> From: Benjamin Poirier <bpoirier@...e.com>
> Sent: Monday, June 17, 2019 1:19 PM
> To: Manish Chopra <manishc@...vell.com>; GR-Linux-NIC-Dev <GR-Linux-
> NIC-Dev@...vell.com>; netdev@...r.kernel.org
> Subject: [PATCH net-next 01/16] qlge: Remove irq_cnt
> 
> qlge uses an irq enable/disable refcounting scheme that is:
> * poorly implemented
> 	Uses a spin_lock to protect accesses to the irq_cnt atomic variable
> * buggy
> 	Breaks when there is not a 1:1 sequence of irq - napi_poll, such as
> 	when using SO_BUSY_POLL.
> * unnecessary
> 	The purpose or irq_cnt is to reduce irq control writes when
> 	multiple work items result from one irq: the irq is re-enabled
> 	after all work is done.
> 	Analysis of the irq handler shows that there is only one case where
> 	there might be two workers scheduled at once, and those have
> 	separate irq masking bits.
> 
> Therefore, remove irq_cnt.
> 
> Additionally, we get a performance improvement:
> perf stat -e cycles -a -r5 super_netperf 100 -H 192.168.33.1 -t TCP_RR
> 
> Before:
> 628560
> 628056
> 622103
> 622744
> 627202
> [...]
>    268,803,947,669      cycles                 ( +-  0.09% )
> 
> After:
> 636300
> 634106
> 634984
> 638555
> 634188
> [...]
>    259,237,291,449      cycles                 ( +-  0.19% )
> 
> Signed-off-by: Benjamin Poirier <bpoirier@...e.com>
> ---
>  drivers/net/ethernet/qlogic/qlge/qlge.h      |  7 --
>  drivers/net/ethernet/qlogic/qlge/qlge_main.c | 98 ++++++--------------
> drivers/net/ethernet/qlogic/qlge/qlge_mpi.c  |  1 -
>  3 files changed, 27 insertions(+), 79 deletions(-)
> 
> diff --git a/drivers/net/ethernet/qlogic/qlge/qlge.h
> b/drivers/net/ethernet/qlogic/qlge/qlge.h
> index ad7c5eb8a3b6..5d9a36deda08 100644
> --- a/drivers/net/ethernet/qlogic/qlge/qlge.h
> +++ b/drivers/net/ethernet/qlogic/qlge/qlge.h
> @@ -1982,11 +1982,6 @@ struct intr_context {
>  	u32 intr_dis_mask;	/* value/mask used to disable this intr */
>  	u32 intr_read_mask;	/* value/mask used to read this intr */
>  	char name[IFNAMSIZ * 2];
> -	atomic_t irq_cnt;	/* irq_cnt is used in single vector
> -				 * environment.  It's incremented for each
> -				 * irq handler that is scheduled.  When each
> -				 * handler finishes it decrements irq_cnt and
> -				 * enables interrupts if it's zero. */
>  	irq_handler_t handler;
>  };
> 
> @@ -2074,7 +2069,6 @@ struct ql_adapter {
>  	u32 port;		/* Port number this adapter */
> 
>  	spinlock_t adapter_lock;
> -	spinlock_t hw_lock;
>  	spinlock_t stats_lock;
> 
>  	/* PCI Bus Relative Register Addresses */ @@ -2235,7 +2229,6 @@
> void ql_mpi_reset_work(struct work_struct *work);  void
> ql_mpi_core_to_log(struct work_struct *work);  int ql_wait_reg_rdy(struct
> ql_adapter *qdev, u32 reg, u32 bit, u32 ebit);  void
> ql_queue_asic_error(struct ql_adapter *qdev);
> -u32 ql_enable_completion_interrupt(struct ql_adapter *qdev, u32 intr);
> void ql_set_ethtool_ops(struct net_device *ndev);  int
> ql_read_xgmac_reg64(struct ql_adapter *qdev, u32 reg, u64 *data);  void
> ql_mpi_idc_work(struct work_struct *work); diff --git
> a/drivers/net/ethernet/qlogic/qlge/qlge_main.c
> b/drivers/net/ethernet/qlogic/qlge/qlge_main.c
> index 6cae33072496..0bfbe11db795 100644
> --- a/drivers/net/ethernet/qlogic/qlge/qlge_main.c
> +++ b/drivers/net/ethernet/qlogic/qlge/qlge_main.c
> @@ -625,75 +625,26 @@ static void ql_disable_interrupts(struct ql_adapter
> *qdev)
>  	ql_write32(qdev, INTR_EN, (INTR_EN_EI << 16));  }
> 
> -/* If we're running with multiple MSI-X vectors then we enable on the fly.
> - * Otherwise, we may have multiple outstanding workers and don't want to
> - * enable until the last one finishes. In this case, the irq_cnt gets
> - * incremented every time we queue a worker and decremented every time
> - * a worker finishes.  Once it hits zero we enable the interrupt.
> - */
> -u32 ql_enable_completion_interrupt(struct ql_adapter *qdev, u32 intr)
> +static void ql_enable_completion_interrupt(struct ql_adapter *qdev, u32
> +intr)
>  {
> -	u32 var = 0;
> -	unsigned long hw_flags = 0;
> -	struct intr_context *ctx = qdev->intr_context + intr;
> -
> -	if (likely(test_bit(QL_MSIX_ENABLED, &qdev->flags) && intr)) {
> -		/* Always enable if we're MSIX multi interrupts and
> -		 * it's not the default (zeroeth) interrupt.
> -		 */
> -		ql_write32(qdev, INTR_EN,
> -			   ctx->intr_en_mask);
> -		var = ql_read32(qdev, STS);
> -		return var;
> -	}
> +	struct intr_context *ctx = &qdev->intr_context[intr];
> 
> -	spin_lock_irqsave(&qdev->hw_lock, hw_flags);
> -	if (atomic_dec_and_test(&ctx->irq_cnt)) {
> -		ql_write32(qdev, INTR_EN,
> -			   ctx->intr_en_mask);
> -		var = ql_read32(qdev, STS);
> -	}
> -	spin_unlock_irqrestore(&qdev->hw_lock, hw_flags);
> -	return var;
> +	ql_write32(qdev, INTR_EN, ctx->intr_en_mask);
>  }
> 
> -static u32 ql_disable_completion_interrupt(struct ql_adapter *qdev, u32
> intr)
> +static void ql_disable_completion_interrupt(struct ql_adapter *qdev,
> +u32 intr)
>  {
> -	u32 var = 0;
> -	struct intr_context *ctx;
> +	struct intr_context *ctx = &qdev->intr_context[intr];
> 
> -	/* HW disables for us if we're MSIX multi interrupts and
> -	 * it's not the default (zeroeth) interrupt.
> -	 */
> -	if (likely(test_bit(QL_MSIX_ENABLED, &qdev->flags) && intr))
> -		return 0;
> -
> -	ctx = qdev->intr_context + intr;
> -	spin_lock(&qdev->hw_lock);
> -	if (!atomic_read(&ctx->irq_cnt)) {
> -		ql_write32(qdev, INTR_EN,
> -		ctx->intr_dis_mask);
> -		var = ql_read32(qdev, STS);
> -	}
> -	atomic_inc(&ctx->irq_cnt);
> -	spin_unlock(&qdev->hw_lock);
> -	return var;
> +	ql_write32(qdev, INTR_EN, ctx->intr_dis_mask);
>  }
> 
>  static void ql_enable_all_completion_interrupts(struct ql_adapter *qdev)  {
>  	int i;
> -	for (i = 0; i < qdev->intr_count; i++) {
> -		/* The enable call does a atomic_dec_and_test
> -		 * and enables only if the result is zero.
> -		 * So we precharge it here.
> -		 */
> -		if (unlikely(!test_bit(QL_MSIX_ENABLED, &qdev->flags) ||
> -			i == 0))
> -			atomic_set(&qdev->intr_context[i].irq_cnt, 1);
> -		ql_enable_completion_interrupt(qdev, i);
> -	}
> 
> +	for (i = 0; i < qdev->intr_count; i++)
> +		ql_enable_completion_interrupt(qdev, i);
>  }
> 
>  static int ql_validate_flash(struct ql_adapter *qdev, u32 size, const char
> *str) @@ -2500,21 +2451,22 @@ static irqreturn_t qlge_isr(int irq, void
> *dev_id)
>  	u32 var;
>  	int work_done = 0;
> 
> -	spin_lock(&qdev->hw_lock);
> -	if (atomic_read(&qdev->intr_context[0].irq_cnt)) {
> -		netif_printk(qdev, intr, KERN_DEBUG, qdev->ndev,
> -			     "Shared Interrupt, Not ours!\n");
> -		spin_unlock(&qdev->hw_lock);
> -		return IRQ_NONE;
> -	}
> -	spin_unlock(&qdev->hw_lock);
> +	/* Experience shows that when using INTx interrupts, the device
> does
> +	 * not always auto-mask the interrupt.
> +	 * When using MSI mode, the interrupt must be explicitly disabled
> +	 * (even though it is auto-masked), otherwise a later command to
> +	 * enable it is not effective.
> +	 */
> +	if (!test_bit(QL_MSIX_ENABLED, &qdev->flags))
> +		ql_disable_completion_interrupt(qdev, 0);
> 
> -	var = ql_disable_completion_interrupt(qdev, intr_context->intr);
> +	var = ql_read32(qdev, STS);
> 
>  	/*
>  	 * Check for fatal error.
>  	 */
>  	if (var & STS_FE) {
> +		ql_disable_completion_interrupt(qdev, 0);
>  		ql_queue_asic_error(qdev);
>  		netdev_err(qdev->ndev, "Got fatal error, STS = %x.\n", var);
>  		var = ql_read32(qdev, ERR_STS);
> @@ -2534,7 +2486,6 @@ static irqreturn_t qlge_isr(int irq, void *dev_id)
>  		 */
>  		netif_err(qdev, intr, qdev->ndev,
>  			  "Got MPI processor interrupt.\n");
> -		ql_disable_completion_interrupt(qdev, intr_context->intr);
>  		ql_write32(qdev, INTR_MASK, (INTR_MASK_PI << 16));
>  		queue_delayed_work_on(smp_processor_id(),
>  				qdev->workqueue, &qdev->mpi_work, 0);
> @@ -2550,11 +2501,18 @@ static irqreturn_t qlge_isr(int irq, void *dev_id)
>  	if (var & intr_context->irq_mask) {
>  		netif_info(qdev, intr, qdev->ndev,
>  			   "Waking handler for rx_ring[0].\n");
> -		ql_disable_completion_interrupt(qdev, intr_context->intr);
>  		napi_schedule(&rx_ring->napi);
>  		work_done++;
> +	} else {
> +		/* Experience shows that the device sometimes signals an
> +		 * interrupt but no work is scheduled from this function.
> +		 * Nevertheless, the interrupt is auto-masked. Therefore, we
> +		 * systematically re-enable the interrupt if we didn't
> +		 * schedule napi.
> +		 */
> +		ql_enable_completion_interrupt(qdev, 0);
>  	}
> -	ql_enable_completion_interrupt(qdev, intr_context->intr);
> +
>  	return work_done ? IRQ_HANDLED : IRQ_NONE;  }
> 
> @@ -3557,7 +3515,6 @@ static int ql_request_irq(struct ql_adapter *qdev)
>  	ql_resolve_queues_to_irqs(qdev);
> 
>  	for (i = 0; i < qdev->intr_count; i++, intr_context++) {
> -		atomic_set(&intr_context->irq_cnt, 0);
>  		if (test_bit(QL_MSIX_ENABLED, &qdev->flags)) {
>  			status = request_irq(qdev->msi_x_entry[i].vector,
>  					     intr_context->handler,
> @@ -4642,7 +4599,6 @@ static int ql_init_device(struct pci_dev *pdev,
> struct net_device *ndev,
>  		goto err_out2;
>  	}
>  	qdev->msg_enable = netif_msg_init(debug, default_msg);
> -	spin_lock_init(&qdev->hw_lock);
>  	spin_lock_init(&qdev->stats_lock);
> 
>  	if (qlge_mpi_coredump) {
> diff --git a/drivers/net/ethernet/qlogic/qlge/qlge_mpi.c
> b/drivers/net/ethernet/qlogic/qlge/qlge_mpi.c
> index 957c72985a06..9e422bbbb6ab 100644
> --- a/drivers/net/ethernet/qlogic/qlge/qlge_mpi.c
> +++ b/drivers/net/ethernet/qlogic/qlge/qlge_mpi.c
> @@ -1257,7 +1257,6 @@ void ql_mpi_work(struct work_struct *work)
>  	/* End polled mode for MPI */
>  	ql_write32(qdev, INTR_MASK, (INTR_MASK_PI << 16) |
> INTR_MASK_PI);
>  	mutex_unlock(&qdev->mpi_mutex);
> -	ql_enable_completion_interrupt(qdev, 0);
>  }
> 
>  void ql_mpi_reset_work(struct work_struct *work)
> --
> 2.21.0

Hello Benjamin, 

Just FYI. I am OOO for a week, so reviewing and testing these patches will take time.

Thanks,
Manish

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