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From:   "Bouska, Zdenek" <zdenek.bouska@siemens.com>
To:     Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>
CC:     Thomas Gleixner <tglx@linutronix.de>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Kiszka, Jan" <jan.kiszka@siemens.com>,
        "linux-rt-users@vger.kernel.org" <linux-rt-users@vger.kernel.org>,
        Nishanth Menon <nm@ti.com>, Puranjay Mohan <p-mohan@ti.com>
Subject: Re: Unfair qspinlocks on ARM64 without LSE atomics => 3ms delay in
 interrupt handling
Thread-Topic: Unfair qspinlocks on ARM64 without LSE atomics => 3ms delay in
 interrupt handling
Thread-Index: AQHZXitnsElEVi8SeUyEotrWHWfO2q8KKDUAgAAS5ICABBn0BA==
Date:   Tue, 28 Mar 2023 09:39:38 +0000
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 <ZB3XaNtVqGtYHHBw@arm.com> <20230324180904.GA28266@willie-the-truck>
In-Reply-To: <20230324180904.GA28266@willie-the-truck>
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> > A longer cpu_relax() here would improve things (on arm64 this function=
=0A=
> > is a no-op) but maybe Thomas or Will have a better idea.=0A=
>=0A=
> I had a pretty gross cpu_relax() implementation using wfe somewhere on=0A=
> LKML, so you could try that if you can dig it up.=0A=
=0A=
Do you mean cpu_relax() implementation from this email [1] from=0A=
Fri, 28 Jul 2017 ?=0A=
=0A=
I tried to rebase it on recent Linux, but it did not even boot for me.=0A=
Only this was printed:=0A=
[    0.000000] Booting Linux on physical CPU 0x0000000000 [0x410fd034]=0A=
[    0=0A=
=0A=
But cpu_relax() implementation from [1] fixes my problem if I use it=0A=
only in irq_finalize_oneshot().=0A=
=0A=
[1] https://lore.kernel.org/lkml/20170728092831.GA24839@arm.com/=0A=
=0A=
Zdenek Bouska=0A=
=0A=
--=0A=
Siemens, s.r.o=0A=
Siemens Advanta Development=