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

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Message-ID: <b4492820-a2d5-7f86-75e4-cb344e050a8f@linux.ibm.com>
Date:   Tue, 25 Oct 2022 15:03:03 -0500
From:   Nick Child <nnac123@...ux.ibm.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, nick.child@....com, dave.taht@...il.com
Subject: Re: [RFC PATCH net-next 0/1] ibmveth: Implement BQL

On 10/25/22 13:41, Jakub Kicinski wrote:
> On Mon, 24 Oct 2022 16:38:27 -0500 Nick Child wrote:

>>  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.
> 
> What qdisc are you using and what "netperf tests" are you running?

Th qdisc is default pfifo_fast.

I have tried the netperf tests described in the patchset which 
introduced BQL[1]. More specifically, 100 low priority netperf 
TCP_STREAMs with 1 high priority TCP_RR. The author of the patchset also 
listed data for number of queued bytes but did not explain how he 
managed to get those measurements.
Additionally, I have tried using flent[2] (a wrapper for netperf) to run 
performance measurements when the system is under considerable load. In 
particular I tried the flent rrul_prio (Realtime Response Under Load - 
Test Prio Queue) and rtt_fair (RTT Fair Realtime Response Under Load) tests.

Again, a positive effect on performance is not as much as a concern for 
me as knowing that BQL is doing is enforcing queue size limits.

Thanks for your help,
Nick

[1] https://lwn.net/Articles/469652/
[2] https://flent.org/