linux-kernel - Re: High-priority softirqs [was: [PATCH] usb: don't offload isochronous urb completions to ksoftirq]

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Message-ID: <20180615174012.m6rqow2sytwgxxrx@linutronix.de>
Date:   Fri, 15 Jun 2018 19:40:13 +0200
From:   Sebastian Sewior <bigeasy@...utronix.de>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Alan Stern <stern@...land.harvard.edu>,
        Mikulas Patocka <mpatocka@...hat.com>,
        Ming Lei <ming.lei@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        USB list <linux-usb@...r.kernel.org>,
        Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: High-priority softirqs [was: [PATCH] usb: don't offload
 isochronous urb completions to ksoftirq]

On 2018-06-15 13:34:28 [-0400], Steven Rostedt wrote:
> On Fri, 15 Jun 2018 19:28:34 +0200 (CEST)
> Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> > One solution to that is to avoid both tasklets and kworkers and change the
> > USB code to make use of threaded interrupt handlers. I.e. handle the fast
> > stuff in the primary (hardirq) handler and delegate the rest to the irq
> > thread. That thread still can offload disk type stuff to a kworker if
> > needed. But the irq thread allows to bring the stuff under scheduler
> > control and experiments which I did a few years ago worked out pretty good.
> 
> If there's any question about this, drivers can request to have their
> interrupt handlers run as threads. This has been added to mainline
> years ago. And it really should be the default solution before pushing
> off to tasklets or kworkers.

 https://lkml.kernel.org/r/20180216170450.yl5owfphuvltstnt@breakpoint.cc

> -- Steve

Sebastian