linux-kernel - Re: [PATCH v2 7/9] sched: define TIF_ALLOW

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Date:   Mon, 02 Oct 2023 18:13:41 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ankur Arora <ankur.a.arora@...cle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
        akpm@...ux-foundation.org, luto@...nel.org, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        willy@...radead.org, mgorman@...e.de, jon.grimm@....com,
        bharata@....com, raghavendra.kt@....com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        jgross@...e.com, andrew.cooper3@...rix.com,
        Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH v2 7/9] sched: define TIF_ALLOW_RESCHED

On Mon, Oct 02 2023 at 10:15, Steven Rostedt wrote:
> On Sat, 23 Sep 2023 03:11:05 +0200
> Thomas Gleixner <tglx@...utronix.de> wrote:
>
>> Though definitely I'm putting a permanent NAK in place for any attempts
>> to duct tape the preempt=NONE model any further by sprinkling more
>> cond*() and whatever warts around.
>
> Well, until we have this fix in, we will still need to sprinkle those
> around when they are triggering watchdog timeouts. I just had to add one
> recently due to a timeout report :-(

cond_resched() sure. But not new flavours of it, like the
[dis]allow_resched() which sparked this discussion.

>> -	TRACE_FLAG_NEED_RESCHED		= 0x04,
>> +	TRACE_FLAG_NEED_RESCHED		= 0x02,
>> +	TRACE_FLAG_NEED_RESCHED_LAZY	= 0x04,
>
> Is LAZY only used for PREEMPT_NONE? Or do we use it for CONFIG_PREEMPT?
> Because, NEED_RESCHED is known, and moving that to bit 2 will break user
> space. Having LAZY replace the IRQS_NOSUPPORT will cause the least
> "breakage".

Either way works for me.

Thanks,

        tglx