netdev - Re: [PATCH linux-next] net: record times of netdev

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Date:   Tue, 6 Dec 2022 10:35:07 +0800 (CST)
From:   <yang.yang29@....com.cn>
To:     <kuba@...nel.org>
Cc:     <davem@...emloft.net>, <edumazet@...gle.com>, <pabeni@...hat.com>,
        <bigeasy@...utronix.de>, <imagedong@...cent.com>,
        <kuniyu@...zon.com>, <petrm@...dia.com>, <liu3101@...due.edu>,
        <wujianguo@...natelecom.cn>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <tedheadster@...il.com>
Subject: Re: [PATCH linux-next] net: record times of netdev_budget exhausted

On Tue, 6 Dec 2022 09:53:05 +0800 (CST) kuba@...nel.org wrote:
> time_squeeze is extremely noisy and annoyingly useless,
> we need to understand exactly what you're doing before
> we accept any changes to this core piece of code.

The author of "Replace 2 jiffies with sysctl netdev_budget_usecs
to enable softirq tuning" is Matthew Whitehead, he said this in
git log: Constants used for tuning are generally a bad idea, especially
as hardware changes over time...For example, a very fast machine
might tune this to 1000 microseconds, while my regression testing
486DX-25 needs it to be 4000 microseconds on a nearly idle network
to prevent time_squeeze from being incremented.

And on my systems there are huge packets on the intranet, and we
came accross with lots of time_squeeze. The idea is that, netdev_budget*
are selections between throughput and real-time. If we care throughput
and not care real-time so much, we may want bigger netdev_budget*.

In this scenario, we want to tune netdev_budget* and see their effect
separately.

By the way, if netdev_budget* are useless, should they be deleted?

Thanks.