APPLIED: [PATCH 0/1][Lunar/linux-azure] Azure: Fix perf regression: remove rx_cqes, tx_cqes counters for MANA

[Tim Gardner]

On 6/5/23 8:48 AM, Tim Gardner wrote:
> BugLink: https://bugs.launchpad.net/bugs/2022940
> 
> SRU Justification
> 
> [Impact]
> 
> net: mana: Fix perf regression: remove rx_cqes, tx_cqes counters
> https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=1919b39fc6eabb9a6f9a51706ff6d03865f5df29
> 
> It resolves a big perf regression.
> 
> More details:
> The apc->eth_stats.rx_cqes is one per NIC (vport), and it's on the
> frequent and parallel code path of all queues. So, r/w into this
> single shared variable by many threads on different CPUs creates a
> lot caching and memory overhead, hence perf regression. And, it's
> not accurate due to the high volume concurrent r/w.
> 
> For example, a workload is iperf with 128 threads, and with RPS
> enabled. We saw perf regression of 25% with the previous patch
> adding the counters. And this patch eliminates the regression.
> 
> Since the error path of mana_poll_rx_cq() already has warnings, so
> keeping the counter and convert it to a per-queue variable is not
> necessary. So, just remove this counter from this high frequency
> code path.
> 
> Also, remove the tx_cqes counter for the same reason. We have
> warnings & other counters for errors on that path, and don't need
> to count every normal cqe processing.
> 
> [Test Plan]
> 
> MSFT tested
> 
> [Regression potential]
> 
> Counters are disappearing that may be in use by user space programs.
> 
> [Other Info]
> 
> SF: #00361807
> 
Applied to lunar linux-azure:master-next. Thanks.

-rtg
-- 
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Tim Gardner
Canonical, Inc