linux-kernel - Re: Softirq priority inversion from "softirq: reduce latencies"

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Message-ID: <20160228170109.GA16322@electric-eye.fr.zoreil.com>
Date:	Sun, 28 Feb 2016 18:01:09 +0100
From:	Francois Romieu <romieu@...zoreil.com>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
Cc:	Peter Hurley <peter@...leysoftware.com>,
	Eric Dumazet <edumazet@...gle.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>,
	dmaengine@...r.kernel.org, John Ogness <john.ogness@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Softirq priority inversion from "softirq: reduce latencies"

Mike Galbraith <umgwanakikbuti@...il.com> :
[...]
> Hrm, relatively new + tasklet woes rings a bell.  Ah, that..
> 
> <quote>
> What's worse is that at the point where this code was written it was
> already well known that tasklets are a steaming pile of crap and
> should die.
> </quote>
> 
> Source thereof https://lwn.net/Articles/588457/

tasklets are ingrained in the dmaengine API (see Documentation/dmaengine/client.txt
and drivers/dma/virt-dma.h::vchan_cookie_complete).

Moving everything to irq context or handling his own sub-{jiffy/ms} timer
while losing async dma doesn't exactly smell like roses either. :o(

-- 
Ueimor