linux-kernel - Re: [RFC] On the Current Troubles of Mainlining Loongson Platform Drivers

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Date:   Thu, 07 Mar 2019 18:22:14 -0300
From:   Alexandre Oliva <lxoliva@...la.org>
To:     Aaro Koskinen <aaro.koskinen@....fi>
Cc:     "Maciej W. Rozycki" <macro@...ux-mips.org>,
        Tom Li <tomli@...li.me>, James Hogan <jhogan@...nel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Huacai Chen <chenhc@...ote.com>,
        Ralf Baechle <ralf@...ux-mips.org>, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC] On the Current Troubles of Mainlining Loongson Platform Drivers

On Mar  7, 2019, Aaro Koskinen <aaro.koskinen@....fi> wrote:

> Hi,
> On Thu, Mar 07, 2019 at 03:41:01AM -0300, Alexandre Oliva wrote:
>> On Feb 17, 2019, "Maciej W. Rozycki" <macro@...ux-mips.org> wrote:
>> 
>> >  Is there an MMIO completion barrier missing there somewhere by any chance 
>> > causing an IRQ that has been handled already to be redelivered because an 
>> > MMIO write meant to clear the IRQ at its origin at handler's completion 
>> > has not reached its destination before interrupts have been reenabled in 
>> > the issuing CPU?  Just a thought.
>> 
>> I've finally got a chance to bisect the IRQ14 (nobody cared) regression
>> on my yeeloong.  It took me to MIPS: Enforce strong ordering for MMIO
>> accessors (commit 3d474dacae72ac0f28228b328cfa953b05484b7f).

> This is interesting, thanks for the research, but I'm afraid it doesn't seem
> to be the root cause.

Oh, I didn't mean to offer anything definitive, just to report the
findings of my investigation so far, since I had no clue when I'd find
another significant time slot to get back onto it.

> Could you check your /proc/interrupts counters after the boot with
> your change?

16k to 18k interrupts after booting up into multi-user mode, including
some idle time (and possibly anacron jobs) in the case that got more
interrupts.  That's not unlike what I get with 4.19.26-gnu.

-- 
Alexandre Oliva, freedom fighter   https://FSFLA.org/blogs/lxo
Be the change, be Free!         FSF Latin America board member
GNU Toolchain Engineer                Free Software Evangelist
Hay que enGNUrecerse, pero sin perder la terGNUra jamás-GNUChe