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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ankur Arora <ankur.a.arora@oracle.com>,
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        Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [PATCH v2 7/9] sched: define TIF_ALLOW_RESCHED
In-Reply-To: <20231002101514.44b9c812@gandalf.local.home>
References: <87ttrngmq0.ffs@tglx> <87jzshhexi.ffs@tglx>
 <20231002101514.44b9c812@gandalf.local.home>
Date:   Mon, 02 Oct 2023 18:13:41 +0200
Message-ID: <87jzs5c896.ffs@tglx>
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On Mon, Oct 02 2023 at 10:15, Steven Rostedt wrote:
> On Sat, 23 Sep 2023 03:11:05 +0200
> Thomas Gleixner <tglx@linutronix.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