linux-kernel - Re: [RFC PATCH 1/4] softirq: Limit vector to a single iteration on IRQ tail

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Date:   Fri, 19 Jan 2018 11:16:25 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     frederic@...nel.org
Cc:     linux-kernel@...r.kernel.org, alexander.levin@...izon.com,
        peterz@...radead.org, mchehab@...pensource.com,
        torvalds@...ux-foundation.org, hannes@...essinduktion.org,
        paulmck@...ux.vnet.ibm.com, wanpeng.li@...mail.com,
        dima@...sta.com, tglx@...utronix.de, akpm@...ux-foundation.org,
        pabeni@...hat.com, rrendec@...sta.com, mingo@...nel.org,
        sgruszka@...hat.com, riel@...hat.com, edumazet@...gle.com
Subject: Re: [RFC PATCH 1/4] softirq: Limit vector to a single iteration on
 IRQ tail

From: Frederic Weisbecker <frederic@...nel.org>
Date: Fri, 19 Jan 2018 16:46:11 +0100

> For now, vectors that get re-enqueued trigger ksoftirqd but they are
> going to be handled by per-vector workqueues on subsequent patches.

Frederic, first of all, thanks for doing all of this work.

So this "get requeued" condition I think will trigger always for
networking tunnel decapsulation.

Each decap will (eventually) do a:

	__raise_softirq_irqoff(NET_RX_SOFTIRQ);

via ____napi_schedule() in net/core/dev.c

Example code path:

	ip_tunnel_rcv()
		gro_cells_receive()
			napi_schedule()
			__napi_schedule()
				____napi_schedule();
				__raise_softirq_irqoff(NET_RX_SOFTIRQ);

Anyways, just FYI...