netdev - Re: [RFC PATCH 1/2] net: Add sysfs files for threaded NAPI.

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Message-ID: <ZG4iDxcQ7BIz0H33@nanopsycho>
Date: Wed, 24 May 2023 16:41:19 +0200
From: Jiri Pirko <jiri@...nulli.us>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	netdev@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
	Kurt Kanzenbach <kurt.kanzenbach@...utronix.de>,
	Paolo Abeni <pabeni@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH 1/2] net: Add sysfs files for threaded NAPI.

Wed, May 24, 2023 at 03:53:27PM CEST, edumazet@...gle.com wrote:
>On Wed, May 24, 2023 at 1:13 PM Sebastian Andrzej Siewior
><bigeasy@...utronix.de> wrote:
>>
>> I've been looking into threaded NAPI. One awkward thing to do is
>> to figure out the thread names, pids in order to adjust the thread
>> priorities and SMP affinity.
>> On PREEMPT_RT the NAPI thread is treated (by the user) the same way as
>> the threaded interrupt which means a dedicate CPU affinity for the
>> thread and a higher task priority to be favoured over other tasks on the
>> CPU. Otherwise the NAPI thread can be preempted by other threads leading
>> to delays in packet delivery.
>> Having to run ps/ grep is awkward to get the PID right. It is not easy
>> to match the interrupt since there is no obvious relation between the
>> IRQ and the NAPI thread.
>> NAPI threads are enabled often to mitigate the problems caused by a
>> "pending" ksoftirqd (which has been mitigated recently by doing softiqrs
>> regardless of ksoftirqd status). There is still the part that the NAPI
>> thread does not use softnet_data::poll_list.
>>
>
>How is interface rename handled ?

Well, having name of interface in sysfs dir/file name is silly, even if
it would be handled correctly. Should not be there.


>
>root@...mazet1:~# ip link show dev dummy0
>4: dummy0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN mode
>DEFAULT group default qlen 1000
>    link/ether f2:38:20:69:b4:ca brd ff:ff:ff:ff:ff:ff
>root@...mazet1:~# ip link set dummy0 name new-name
>root@...mazet1:~# ip link show dev dummy0
>Device "dummy0" does not exist.
>root@...mazet1:~# ip link show dev new-name
>4: new-name: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN mode
>DEFAULT group default qlen 1000
>    link/ether f2:38:20:69:b4:ca brd ff:ff:ff:ff:ff:ff
>
>Thanks.
>