linux-kernel - Re: [RFC PATCH 0/4] softirq: Per vector threading v3

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Message-Id: <20180124.100558.97132829347179555.davem@davemloft.net>
Date:   Wed, 24 Jan 2018 10:05:58 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     pabeni@...hat.com
Cc:     torvalds@...ux-foundation.org, frederic@...nel.org,
        linux-kernel@...r.kernel.org, alexander.levin@...izon.com,
        peterz@...radead.org, mchehab@...pensource.com,
        hannes@...essinduktion.org, paulmck@...ux.vnet.ibm.com,
        wanpeng.li@...mail.com, dima@...sta.com, tglx@...utronix.de,
        akpm@...ux-foundation.org, rrendec@...sta.com, mingo@...nel.org,
        sgruszka@...hat.com, riel@...hat.com, edumazet@...gle.com,
        nks.gnu@...il.com
Subject: Re: [RFC PATCH 0/4] softirq: Per vector threading v3

From: Paolo Abeni <pabeni@...hat.com>
Date: Wed, 24 Jan 2018 15:54:05 +0100

> Niklas suggested a possible relation with CONFIG_IRQ_TIME_ACCOUNTING=y
> and indeed he was right.
> 
> The patched kernel under test had CONFIG_IRQ_TIME_ACCOUNTING set, and
> very little CPU time was accounted to the kworker:
> 
> [2125 is the relevant kworker's pid]
> grep sum_exec_runtime /proc/2125/sched; sleep 10; grep sum_exec_runtime /proc/2125/sched
> se.sum_exec_runtime                          :         13408.239286
> se.sum_exec_runtime                          :         13456.907197
> 
> despite such process was processing a lot of packets and basically
> burning a CPU.

So IRQ_TIME_ACCOUNTING makes the scheduler think that the worker
threads are using nearly no task time at all.

The existing ksoftirqd code should hit the same problem, right?