From: Jan Kiszka <jan.kiszka@siemens.com>
To: Thomas Gleixner <tglx@linutronix.de>,
"Bouska, Zdenek" <zdenek.bouska@siemens.com>,
Will Deacon <will@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>
Cc: "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
Date: Thu, 27 Apr 2023 15:14:47 +0200 [thread overview]
Message-ID: <19641ab0-ab6a-9af7-8c64-34030e187848@siemens.com> (raw)
In-Reply-To: <87pm7qxrg6.ffs@tglx>
On 26.04.23 23:29, Thomas Gleixner wrote:
> On Wed, Apr 26 2023 at 12:03, Zdenek Bouska wrote:
>> following patch is my current approach for fixing this issue. I introduced
>> big_cpu_relax(), which uses Will's implementation [1] on ARM64 without
>> LSE atomics and original cpu_relax() on any other CPU.
>
> Why is this interrupt handling specific? Just because it's the place
> where you observed it?
>
> That's a general issue for any code which uses atomics for forward
> progress. LL/SC simply does not guarantee that.
>
> So if that helps, then this needs to be addressed globaly and not with
> some crude hack in the interrupt handling code.
My impression is that the retry loop of irq_finalize_oneshot is
particularly susceptible to that issue due to the high acquire/relax
pressure and inter-dependency between holder and waiter it generates -
which does not mean it cannot occur in other places.
Are we aware of other concrete case where it bites? Even with just
"normal" contented spin_lock usage?
>
>> Anyone has a better idea how to solve this issue properly?
>
> Use hardware with LSE atomics :)
That would generate tons of waste of current electronic devices without
it - not very fashionable anymore. ;)
Jan
--
Siemens AG, Technology
Competence Center Embedded Linux
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next prev parent reply other threads:[~2023-04-27 13:16 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <AS1PR10MB567534190B05A4493674173BEB659@AS1PR10MB5675.EURPRD10.PROD.OUTLOOK.COM>
2023-04-26 21:29 ` Unfair qspinlocks on ARM64 without LSE atomics => 3ms delay in interrupt handling Thomas Gleixner
2023-04-27 9:38 ` Bouska, Zdenek
2023-04-27 10:06 ` Will Deacon
2023-04-27 13:14 ` Jan Kiszka [this message]
2023-04-27 13:45 ` Kurt Kanzenbach
2023-04-28 7:30 ` Sebastian Andrzej Siewior
2023-04-28 7:37 ` Kurt Kanzenbach
2023-03-24 8:43 Bouska, Zdenek
2023-03-24 17:01 ` Catalin Marinas
2023-03-24 18:09 ` Will Deacon
2023-03-28 9:39 ` Bouska, Zdenek
2023-03-27 5:44 ` Bouska, Zdenek
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