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Date: Wed, 24 May 2023 08:55:07 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: netdev@vger.kernel.org, Eric Dumazet <edumazet@google.com>, Kurt
 Kanzenbach <kurt.kanzenbach@linutronix.de>, Paolo Abeni
 <pabeni@redhat.com>, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [RFC PATCH 1/2] net: Add sysfs files for threaded NAPI.
Message-ID: <20230524085507.3f38c758@kernel.org>
In-Reply-To: <20230524111259.1323415-2-bigeasy@linutronix.de>
References: <20230524111259.1323415-1-bigeasy@linutronix.de>
	<20230524111259.1323415-2-bigeasy@linutronix.de>
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On Wed, 24 May 2023 13:12:58 +0200 Sebastian Andrzej Siewior 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.

This needs to go to the netdev netlink family, not sysfs.
There's much more information about NAPI to expose and sysfs will
quickly start showing its limitations.