[SRU][R:aws/Q:aws][PATCH 0/1] Set ENA_INTR_INITIAL_TX_INTERVAL_USECS to 64

[Magali Lemes]

BugLink: https://bugs.launchpad.net/bugs/2144038

[Impact]
R:aws and Q:aws kernels set ENA_INTR_INITIAL_TX_INTERVAL_USECS to 0 in
drivers/net/ethernet/amazon/ena/ena_com.h, disabling TX interrupt
coalescing. This causes 10-25% Nginx performance regression compared to
the Ubuntu 22.04 6.8 kernel, which correctly uses tx-usecs=64 matching
the upstream default. This is likely to impact any network
throughput-heavy application running on EC2.

[Fix]
Revert the SAUCE patch setting ENA_INTR_INITIAL_TX_INTERVAL_USECS to 0.

[Test Plan]
Launch an AWS EC2 instance that uses the ENA driver (e.g. m8g.2xlarge or
m8i.2xlarge) running Ubuntu 24.04 to host the Nginx server. Launch a
second instance to act as the load generator.

On the server, boot a 6.17+ AWS kernel without the patch, verify
tx-usecs is 0 (ethtool -c <interface-name> | grep tx-usecs), then
generate load from the client using wrk (wrk -t 8 -c 1000 -d 60s
http://<SERVER-IP>) and record the RPS. Again in the server, reboot into
a patched 6.17+ AWS kernel, confirm tx-usecs is 64, and rerun the same
workload. The patched kernel should show significantly higher RPS.

[Where problems could occur]
This change only affects the ENA driver, modifying the default TX
interrupt coalescing value (tx-usecs) from 0 back to 64, which may
introduce a small increase in packet transmission latency.

Magali Lemes (1):
  Revert "UBUNTU: SAUCE: net: ena: fix too long default tx interrupt
    moderation interval"

 drivers/net/ethernet/amazon/ena/ena_com.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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2.43.0