linux-kernel - Re: [PATCH v8 4/5] locking/qspinlock: Introduce starvation avoidance into CNA

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Message-ID: <20200125112039.GX11457@worktop.programming.kicks-ass.net>
Date:   Sat, 25 Jan 2020 12:20:39 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Alex Kogan <alex.kogan@...cle.com>, linux@...linux.org.uk,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, hpa@...or.com, x86@...nel.org,
        Hanjun Guo <guohanjun@...wei.com>,
        Jan Glauber <jglauber@...vell.com>,
        Steven Sistare <steven.sistare@...cle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        dave.dice@...cle.com
Subject: Re: [PATCH v8 4/5] locking/qspinlock: Introduce starvation avoidance
 into CNA

On Fri, Jan 24, 2020 at 01:51:34PM -0500, Waiman Long wrote:

< 71 lines of garbage >

> > You can use the in_task() macro in include/linux/preempt.h. This is
> > just a percpu preempt_count read and test. If in_task() is false, it
> > is in a {soft|hard}irq or nmi context. If it is true, you can check
> > the rt_task() macro to see if it is an RT task. That will access to
> > the current task structure. So it may cost a little bit more if you
> > want to handle the RT task the same way.
> >
> We may not need to do that for softIRQ context. If that is the case, you
> can use in_irq() which checks for hardirq and nmi only. Peter, what is
> your thought on that?

Can you lot please start trimming emails when you reply?