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ibmvnic: Only record tx completed bytes once per handler

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Byte Queue Limits depends on dql_completed being called once per tx
completion round in order to adjust its algorithm appropriately. The
dql->limit value is an approximation of the amount of bytes that the NIC
can consume per irq interval. If this approximation is too high then the
NIC will become over-saturated. Too low and the NIC will starve.

The dql->limit depends on dql->prev-* stats to calculate an optimal
value. If dql_completed() is called more than once per irq handler then
those prev-* values become unreliable (because they are not an accurate
representation of the previous state of the NIC) resulting in a
sub-optimal limit value.

Therefore, move the call to netdev_tx_completed_queue() to the end of
ibmvnic_complete_tx().

When performing 150 sessions of TCP rr (request-response 1 byte packets)
workloads, one could observe:
  PREVIOUSLY: - limit and inflight values hovering around 130
              - transaction rate of around 750k pps.

  NOW:        - limit rises and falls in response to inflight (130-900)
              - transaction rate of around 1M pps (33% improvement)

Signed-off-by: Nick Child <nnac123@linux.ibm.com>
Link: https://patch.msgid.link/20240807211809.1259563-7-nnac123@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Nick Child 2024-08-07 16:18:08 -05:00 committed by Jakub Kicinski
parent 74839f7a82
commit 1c33e29245
1 changed files with 5 additions and 7 deletions
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12
drivers/net/ethernet/ibm/ibmvnic.c
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@ -4189,20 +4189,17 @@ static int ibmvnic_complete_tx(struct ibmvnic_adapter *adapter,
struct ibmvnic_sub_crq_queue *scrq)
{
struct device *dev = &adapter->vdev->dev;
int num_packets = 0, total_bytes = 0;
struct ibmvnic_tx_pool *tx_pool;
struct ibmvnic_tx_buff *txbuff;
struct netdev_queue *txq;
union sub_crq *next;
int index;
int i;
int index, i;
restart_loop:
while (pending_scrq(adapter, scrq)) {
unsigned int pool = scrq->pool_index;
int num_entries = 0;
int total_bytes = 0;
int num_packets = 0;
next = ibmvnic_next_scrq(adapter, scrq);
for (i = 0; i < next->tx_comp.num_comps; i++) {
index = be32_to_cpu(next->tx_comp.correlators[i]);
@ -4238,8 +4235,6 @@ restart_loop:
/* remove tx_comp scrq*/
next->tx_comp.first = 0;
txq = netdev_get_tx_queue(adapter->netdev, scrq->pool_index);
netdev_tx_completed_queue(txq, num_packets, total_bytes);
if (atomic_sub_return(num_entries, &scrq->used) <=
(adapter->req_tx_entries_per_subcrq / 2) &&
@ -4264,6 +4259,9 @@ restart_loop:
goto restart_loop;
}
txq = netdev_get_tx_queue(adapter->netdev, scrq->pool_index);
netdev_tx_completed_queue(txq, num_packets, total_bytes);
return 0;
}