Subject: Re: [next-queue v2 2/4] i40e: Record number TXes cleaned during NAPI

From: Joe Damato <[email-masked]>
Date: Wed, 5 Oct 2022 18:00:24 -0700

On Wed, Oct 05, 2022 at 05:31:04PM -0700, Joe Damato wrote:
> 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 <[email-masked]>
> > >---
> > >  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.

I suppose the alternative is to only fire the tracepoint when *not* in XDP.
Then the changes to the XDP stuff can be dropped and a separate set of
tracepoints for XDP can be created in the future.

That might reduce the complexity a bit, and will probably still be pretty
useful for people tuning their non-XDP workloads.