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From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     Kurt Kanzenbach <kurt@linutronix.de>
Cc:     Jan Kiszka <jan.kiszka@siemens.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Bouska, Zdenek" <zdenek.bouska@siemens.com>,
        Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "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
Message-ID: <20230428073016.YfrIGGoN@linutronix.de>
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On 2023-04-27 15:45:09 [+0200], Kurt Kanzenbach wrote:
> > Are we aware of other concrete case where it bites? Even with just
> > "normal" contented spin_lock usage?
> 
> Well, some years ago I've observed a similar problem with ARM64
> spinlocks, cpu_relax() and retry loops (in the futex code). It also
> generated latency spikes up to 2-3ms. Back then, it was easily
> reproducible using stress-ng --ptrace 4.

That was fixed by
	https://patchwork.kernel.org/project/linux-arm-kernel/patch/1399528508-2806-1-git-send-email-arjun.kv@samsung.com

if my memory serves me well.

> Thanks,
> Kurt

Sebastian