linux-kernel - Re: [PATCH v6 1/1] MIPS: Fix idle VS timer enqueue

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Message-ID: <Z93Vj7BLTEvgWwda@pavilion.home>
Date: Fri, 21 Mar 2025 22:09:35 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: "Maciej W. Rozycki" <macro@...am.me.uk>
Cc: Marco Crivellari <marco.crivellari@...e.com>,
	linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Huacai Chen <chenhuacai@...nel.org>
Subject: Re: [PATCH v6 1/1] MIPS: Fix idle VS timer enqueue

Le Fri, Mar 21, 2025 at 11:53:54AM +0000, Maciej W. Rozycki a écrit :
> On Sat, 15 Mar 2025, Marco Crivellari wrote:
> 
> > diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S
> > index a572ce36a24f..4e012421d00f 100644
> > --- a/arch/mips/kernel/genex.S
> > +++ b/arch/mips/kernel/genex.S
> > @@ -104,27 +104,30 @@ handle_vcei:
> >  
> >  	__FINIT
> >  
> > -	.align	5	/* 32 byte rollback region */
> > +	.align	5
> >  LEAF(__r4k_wait)
> >  	.set	push
> >  	.set	noreorder
> > -	/* start of rollback region */
> > -	LONG_L	t0, TI_FLAGS($28)
> > -	nop
> > -	andi	t0, _TIF_NEED_RESCHED
> > -	bnez	t0, 1f
> > -	 nop
> > -	nop
> > -	nop
> > -#ifdef CONFIG_CPU_MICROMIPS
> > -	nop
> > -	nop
> > -	nop
> > -	nop
> > -#endif
> > +	/* Start of idle interrupt region. */
> > +	MFC0	t0, CP0_STATUS
> > +	/* Enable interrupt. */
> > +	ori 	t0, 0x1f
> 
>  This instruction sequence still suffers from the coprocessor move delay 
> hazard.  How many times do I need to request to get it fixed (counting 
> three so far)?

This is because your request had follow-ups from Huacai and Marco that
were left unanswered:

     https://lore.kernel.org/all/CAAhV-H5ptAzHTPAr1bxrgByZrnFmMK8zJ68Z++RwC=NHWjqZmw@mail.gmail.com/
     https://lore.kernel.org/all/CAAofZF4HAczyRmuRe-JmQ2wcZatevLwGTOMLf1V1okGbj7q5Wg@mail.gmail.com/

We have detected this longstanding architecture specific timer handling bug on
loongson and MIPS and we could have just dropped a report and let you guys deal with
it. Instead we decided to spend time ourselves (especially Marco) working on
fixes for these architectures we don't run and which we are not familiar with,
alongway taking reviews seriously and patiently re-iterating accordingly.

So please be gentle with us.

Thanks.