netdev - [RFC PATCH net-next 0/1] ibmveth: Implement BQL

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Date:   Mon, 24 Oct 2022 16:38:27 -0500
From:   Nick Child <nnac123@...ux.ibm.com>
To:     netdev@...r.kernel.org
Cc:     nick.child@....com, dave.taht@...il.com,
        Nick Child <nnac123@...ux.ibm.com>
Subject: [RFC PATCH net-next 0/1] ibmveth: Implement BQL

Hello,

Labeled as RFC because I am unsure if adding Byte Queue Limits (BQL) is
positively effecting the ibmveth driver. BQL is common among network
drivers so I would like to incorporate it into the virtual ethernet
driver, ibmveth. But I am having trouble measuring its effects.

>From my understanding (and please correct me if I am wrong), BQL will 
use the number of packets sent to the NIC to approximate the minimum
number of packets to enqueue to a netdev_queue without starving the NIC.
As a result, bufferbloat in the networking queues are minimized which
may allow for smaller latencies.

After performing various netperf tests under differing loads and
priorities, I do not see any performance effect when comparing the
driver with and without BQL. The ibmveth driver is a virtual driver
which has an abstracted view of the NIC so I am comfortable without
seeing any performance deltas. That being said, I would like to know if
BQL is actually being enforced in some way. In other words, I would
like to observe a change in the number of queued bytes during BQL
implementations. Does anyone know of a mechanism to measure the length
of a netdev_queue?

I tried creating a BPF script[1] to track the bytes in a netdev_queue
but again am not seeing any difference with and without BQL. I do not
believe anything is wrong with BQL (it is more likely that my tracing
is bad) but I would like to have some evidence of BQL having a
positive effect on the device. Any recommendations or advice would be
greatly appreciated.
Thanks.

[1] https://github.com/nick-child-ibm/bpf_scripts/blob/main/bpftrace_queued_bytes.bt 

Nick Child (1):
  ibmveth: Implement BQL

 drivers/net/ethernet/ibm/ibmveth.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

-- 
2.31.1