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

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Message-ID: <1456638957.3676.12.camel@gmail.com>
Date:	Sun, 28 Feb 2016 06:55:57 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Peter Hurley <peter@...leysoftware.com>,
	Eric Dumazet <edumazet@...gle.com>
Cc:	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"

On Sat, 2016-02-27 at 10:19 -0800, Peter Hurley wrote:
> Hi Eric,
> 
> For a while now, we've been struggling to understand why we've been
> observing missed uart rx DMA.
> 
> Because both the uart driver (omap8250) and the dmaengine driver
> (edma) were (relatively) new, we assumed there was some race between
> starting a new rx DMA and processing the previous one.

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/

	-Mike