netdev - Re: [PATCH net-next] net: axienet: Use NAPI for TX completion path

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Date:   Wed, 4 May 2022 19:20:28 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Radhey Shyam Pandey <radheys@...inx.com>,
        Robert Hancock <robert.hancock@...ian.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        Michal Simek <michals@...inx.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Harini Katakam <harinik@...inx.com>
Subject: Re: [PATCH net-next] net: axienet: Use NAPI for TX completion path

On Mon, 2 May 2022 19:30:51 +0000 Radhey Shyam Pandey wrote:
> > This driver was using the TX IRQ handler to perform all TX completion
> > tasks. Under heavy TX network load, this can cause significant irqs-off
> > latencies (found to be in the hundreds of microseconds using ftrace).
> > This can cause other issues, such as overrunning serial UART FIFOs when
> > using high baud rates with limited UART FIFO sizes.
> > 
> > Switch to using the NAPI poll handler to perform the TX completion work
> > to get this out of hard IRQ context and avoid the IRQ latency impact.  
> 
> Thanks for the patch. I assume for simulating heavy network load we
> are using netperf/iperf. Do we have some details on the benchmark
> before and after adding TX NAPI? I want to see the impact on
> throughput.

Seems like a reasonable ask, let's get the patch reposted 
with the numbers in the commit message.