linux-kernel - Re: Unfair qspinlocks on ARM64 without LSE atomics => 3ms delay in interrupt handling

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Date:   Thu, 27 Apr 2023 09:38:59 +0000
From:   "Bouska, Zdenek" <zdenek.bouska@...mens.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>
CC:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Kiszka, Jan" <jan.kiszka@...mens.com>,
        "linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>,
        Nishanth Menon <nm@...com>, Puranjay Mohan <p-mohan@...com>
Subject: Re: Unfair qspinlocks on ARM64 without LSE atomics => 3ms delay in
 interrupt handling

> Why is this interrupt handling specific? Just because it's the place
> where you observed it?
Yes.

> So if that helps, then this needs to be addressed globaly and not with
> some crude hack in the interrupt handling code.
I just wrote, what helps for me. I didn't mean it as a proposal for merge.
Sorry for confusion.

I tried using Will's cpu_relax() implementation [1] everywhere but I was not 
successful with that yet. ARM64's VDSO makes it complicating and even
if I left original cpu_relax() just in VDSO, Linux did not boot for me.

Thank you all!

[1] https://lore.kernel.org/lkml/20170728092831.GA24839@arm.com/

Zdenek Bouska

--
Siemens, s.r.o
Siemens Advanta Development