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From: Thomas Gleixner <tglx@linutronix.de>
To: "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>,
	"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
Date: Wed, 26 Apr 2023 23:29:45 +0200	[thread overview]
Message-ID: <87pm7qxrg6.ffs@tglx> (raw)
In-Reply-To: <AS1PR10MB567534190B05A4493674173BEB659@AS1PR10MB5675.EURPRD10.PROD.OUTLOOK.COM>

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.

> Anyone has a better idea how to solve this issue properly?

Use hardware with LSE atomics :)

Thanks,

        tglx

WARNING: multiple messages have this Message-ID (diff)
From: Thomas Gleixner <tglx@linutronix.de>
To: "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>,
	"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
Date: Wed, 26 Apr 2023 23:29:45 +0200	[thread overview]
Message-ID: <87pm7qxrg6.ffs@tglx> (raw)
In-Reply-To: <AS1PR10MB567534190B05A4493674173BEB659@AS1PR10MB5675.EURPRD10.PROD.OUTLOOK.COM>

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.

> Anyone has a better idea how to solve this issue properly?

Use hardware with LSE atomics :)

Thanks,

        tglx

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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2023-04-26 21:30 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-04-26 12:03 Unfair qspinlocks on ARM64 without LSE atomics => 3ms delay in interrupt handling Bouska, Zdenek
2023-04-26 21:29 ` Thomas Gleixner [this message]
2023-04-26 21:29   ` Thomas Gleixner
2023-04-27  9:38   ` Bouska, Zdenek
2023-04-27  9:38     ` Bouska, Zdenek
2023-04-27 10:06     ` Will Deacon
2023-04-27 10:06       ` Will Deacon
2023-04-27 13:14   ` Jan Kiszka
2023-04-27 13:14     ` Jan Kiszka
2023-04-27 13:45     ` Kurt Kanzenbach
2023-04-27 13:45       ` Kurt Kanzenbach
2023-04-28  7:30       ` Sebastian Andrzej Siewior
2023-04-28  7:30         ` Sebastian Andrzej Siewior
2023-04-28  7:37         ` Kurt Kanzenbach
2023-04-28  7:37           ` Kurt Kanzenbach
  -- strict thread matches above, loose matches on Subject: below --
2023-03-24  8:43 Bouska, Zdenek
2023-03-24  8:43 ` Bouska, Zdenek
2023-03-24 17:01 ` Catalin Marinas
2023-03-24 17:01   ` Catalin Marinas
2023-03-24 18:09   ` Will Deacon
2023-03-24 18:09     ` Will Deacon
2023-03-28  9:39     ` Bouska, Zdenek
2023-03-28  9:39       ` Bouska, Zdenek
2023-03-27  5:44   ` Bouska, Zdenek
2023-03-27  5:44     ` Bouska, Zdenek

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