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

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Message-ID: <20190307202156.GB30189@darkstar.musicnaut.iki.fi>
Date:   Thu, 7 Mar 2019 22:21:56 +0200
From:   Aaro Koskinen <aaro.koskinen@....fi>
To:     Alexandre Oliva <lxoliva@...la.org>
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

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.

While your patch seems to help also on Mini-PC (only briefly tested with
a dozen of reboots), there's still excessive amount of interrupts during
the boot - I'm getting something like 50000-70000, while with the old
IDE driver it's around 2500.

~ # cat /proc/irq/14/spurious 
count 57805
unhandled 57799
last_unhandled 4294673092 ms
~ # cat /proc/interrupts 
           CPU0       
  2:          0    XT-PIC   2  cascade
  3:        174    XT-PIC   3  ttyS0
  5:      14653    XT-PIC   5  timer
 11:          0    XT-PIC  11  ehci_hcd:usb1, ohci_hcd:usb2
 14:      57805    XT-PIC  14  pata_amd
 15:          0    XT-PIC  15  pata_amd
 18:          0      MIPS   2  cascade
 22:          0      MIPS   6  cascade
ERR:          0

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

A.