Date:   Wed, 5 Oct 2022 17:31:05 -0700
From:   Joe Damato <jdamato@...tly.com>
To:     "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
Cc:     intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
        kuba@...nel.org, davem@...emloft.net, anthony.l.nguyen@...el.com,
        jesse.brandeburg@...el.com, maciej.fijalkowski@...el.com
Subject: Re: [next-queue v2 2/4] i40e: Record number TXes cleaned during NAPI

On Wed, Oct 05, 2022 at 07:16:56PM -0500, Samudrala, Sridhar wrote:
> On 10/5/2022 4:21 PM, Joe Damato wrote:
> >Update i40e_clean_tx_irq to take an out parameter (tx_cleaned) which stores
> >the number TXs cleaned.
> >
> >Likewise, update i40e_clean_xdp_tx_irq and i40e_xmit_zc to do the same.
> >
> >Care has been taken to avoid changing the control flow of any functions
> >involved.
> >
> >Signed-off-by: Joe Damato <jdamato@...tly.com>
> >---
> >  drivers/net/ethernet/intel/i40e/i40e_txrx.c | 16 +++++++++++-----
> >  drivers/net/ethernet/intel/i40e/i40e_xsk.c  | 15 +++++++++++----
> >  drivers/net/ethernet/intel/i40e/i40e_xsk.h  |  3 ++-
> >  3 files changed, 24 insertions(+), 10 deletions(-)
> >
> >diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> >index b97c95f..a2cc98e 100644
> >--- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> >+++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> >@@ -923,11 +923,13 @@ void i40e_detect_recover_hung(struct i40e_vsi *vsi)
> >   * @vsi: the VSI we care about
> >   * @tx_ring: Tx ring to clean
> >   * @napi_budget: Used to determine if we are in netpoll
> >+ * @tx_cleaned: Out parameter set to the number of TXes cleaned
> >   *
> >   * Returns true if there's any budget left (e.g. the clean is finished)
> >   **/
> >  static bool i40e_clean_tx_irq(struct i40e_vsi *vsi,
> >-			      struct i40e_ring *tx_ring, int napi_budget)
> >+			      struct i40e_ring *tx_ring, int napi_budget,
> >+			      unsigned int *tx_cleaned)
> >  {
> >  	int i = tx_ring->next_to_clean;
> >  	struct i40e_tx_buffer *tx_buf;
> >@@ -1026,7 +1028,7 @@ static bool i40e_clean_tx_irq(struct i40e_vsi *vsi,
> >  	i40e_arm_wb(tx_ring, vsi, budget);
> >  	if (ring_is_xdp(tx_ring))
> >-		return !!budget;
> >+		goto out;
> >  	/* notify netdev of completed buffers */
> >  	netdev_tx_completed_queue(txring_txq(tx_ring),
> >@@ -1048,6 +1050,8 @@ static bool i40e_clean_tx_irq(struct i40e_vsi *vsi,
> >  		}
> >  	}
> >+out:
> >+	*tx_cleaned = total_packets;
> >  	return !!budget;
> >  }
> >@@ -2689,10 +2693,12 @@ int i40e_napi_poll(struct napi_struct *napi, int budget)
> >  			       container_of(napi, struct i40e_q_vector, napi);
> >  	struct i40e_vsi *vsi = q_vector->vsi;
> >  	struct i40e_ring *ring;
> >+	bool tx_clean_complete = true;
> >  	bool clean_complete = true;
> >  	bool arm_wb = false;
> >  	int budget_per_ring;
> >  	int work_done = 0;
> >+	unsigned int tx_cleaned = 0;
> >  	if (test_bit(__I40E_VSI_DOWN, vsi->state)) {
> >  		napi_complete(napi);
> >@@ -2704,11 +2710,11 @@ int i40e_napi_poll(struct napi_struct *napi, int budget)
> >  	 */
> >  	i40e_for_each_ring(ring, q_vector->tx) {
> >  		bool wd = ring->xsk_pool ?
> >-			  i40e_clean_xdp_tx_irq(vsi, ring) :
> >-			  i40e_clean_tx_irq(vsi, ring, budget);
> >+			  i40e_clean_xdp_tx_irq(vsi, ring, &tx_cleaned) :
> >+			  i40e_clean_tx_irq(vsi, ring, budget, &tx_cleaned);
> >  		if (!wd) {
> >-			clean_complete = false;
> >+			clean_complete = tx_clean_complete = false;
> >  			continue;
> >  		}
> >  		arm_wb |= ring->arm_wb;
> >diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> >index 790aaeff..f98ce7e4 100644
> >--- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> >+++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> >@@ -530,18 +530,22 @@ static void i40e_set_rs_bit(struct i40e_ring *xdp_ring)
> >   * i40e_xmit_zc - Performs zero-copy Tx AF_XDP
> >   * @xdp_ring: XDP Tx ring
> >   * @budget: NAPI budget
> >+ * @tx_cleaned: Out parameter of the TX packets processed
> >   *
> >   * Returns true if the work is finished.
> >   **/
> >-static bool i40e_xmit_zc(struct i40e_ring *xdp_ring, unsigned int budget)
> >+static bool i40e_xmit_zc(struct i40e_ring *xdp_ring, unsigned int budget,
> >+			 unsigned int *tx_cleaned)
> >  {
> >  	struct xdp_desc *descs = xdp_ring->xsk_pool->tx_descs;
> >  	u32 nb_pkts, nb_processed = 0;
> >  	unsigned int total_bytes = 0;
> >  	nb_pkts = xsk_tx_peek_release_desc_batch(xdp_ring->xsk_pool, budget);
> >-	if (!nb_pkts)
> >+	if (!nb_pkts) {
> >+		*tx_cleaned = 0;
> >  		return true;
> >+	}
> >  	if (xdp_ring->next_to_use + nb_pkts >= xdp_ring->count) {
> >  		nb_processed = xdp_ring->count - xdp_ring->next_to_use;
> >@@ -558,6 +562,7 @@ static bool i40e_xmit_zc(struct i40e_ring *xdp_ring, unsigned int budget)
> >  	i40e_update_tx_stats(xdp_ring, nb_pkts, total_bytes);
> >+	*tx_cleaned = nb_pkts;
> 
> With XDP, I don't think we should count these as tx_cleaned packets. These are transmitted
> packets. The tx_cleaned would be the xsk_frames counter in i40e_clean_xdp_tx_irq
> May be we need 2 counters for xdp.

I think there's two issues you are describing, which are separate in my
mind.

  1.) The name "tx_cleaned", and
  2.) Whether nb_pkts is the right thing to write as the out param.

For #1: I'm OK to change the name if that's the blocker here; please
suggest a suitable alternative that you'll accept.

For #2: nb_pkts is, IMO, the right value to bubble up to the tracepoint because
nb_pkts affects clean_complete in i40e_napi_poll which in turn determines
whether or not polling mode is entered.

The purpose of the tracepoint is to determine when/why/how you are entering
polling mode, so if nb_pkts plays a role in that calculation, it's the
right number to output.


> >  	return nb_pkts < budget;
> >  }
> >@@ -581,10 +586,12 @@ static void i40e_clean_xdp_tx_buffer(struct i40e_ring *tx_ring,
> >   * i40e_clean_xdp_tx_irq - Completes AF_XDP entries, and cleans XDP entries
> >   * @vsi: Current VSI
> >   * @tx_ring: XDP Tx ring
> >+ * @tx_cleaned: out parameter of number of TXes cleaned
> >   *
> >   * Returns true if cleanup/tranmission is done.
> >   **/
> >-bool i40e_clean_xdp_tx_irq(struct i40e_vsi *vsi, struct i40e_ring *tx_ring)
> >+bool i40e_clean_xdp_tx_irq(struct i40e_vsi *vsi, struct i40e_ring *tx_ring,
> >+			   unsigned int *tx_cleaned)
> >  {
> >  	struct xsk_buff_pool *bp = tx_ring->xsk_pool;
> >  	u32 i, completed_frames, xsk_frames = 0;
> >@@ -634,7 +641,7 @@ bool i40e_clean_xdp_tx_irq(struct i40e_vsi *vsi, struct i40e_ring *tx_ring)
> >  	if (xsk_uses_need_wakeup(tx_ring->xsk_pool))
> >  		xsk_set_tx_need_wakeup(tx_ring->xsk_pool);
> >-	return i40e_xmit_zc(tx_ring, I40E_DESC_UNUSED(tx_ring));
> >+	return i40e_xmit_zc(tx_ring, I40E_DESC_UNUSED(tx_ring), tx_cleaned);
> >  }
> >  /**
> >diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.h b/drivers/net/ethernet/intel/i40e/i40e_xsk.h
> >index 821df24..396ed11 100644
> >--- a/drivers/net/ethernet/intel/i40e/i40e_xsk.h
> >+++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.h
> >@@ -30,7 +30,8 @@ int i40e_xsk_pool_setup(struct i40e_vsi *vsi, struct xsk_buff_pool *pool,
> >  bool i40e_alloc_rx_buffers_zc(struct i40e_ring *rx_ring, u16 cleaned_count);
> >  int i40e_clean_rx_irq_zc(struct i40e_ring *rx_ring, int budget);
> >-bool i40e_clean_xdp_tx_irq(struct i40e_vsi *vsi, struct i40e_ring *tx_ring);
> >+bool i40e_clean_xdp_tx_irq(struct i40e_vsi *vsi, struct i40e_ring *tx_ring,
> >+			   unsigned int *tx_cleaned);
> >  int i40e_xsk_wakeup(struct net_device *dev, u32 queue_id, u32 flags);
> >  int i40e_realloc_rx_bi_zc(struct i40e_vsi *vsi, bool zc);
> >  void i40e_clear_rx_bi_zc(struct i40e_ring *rx_ring);
> 

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