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From: Tony Lindgren <tony@atomide.com>
To: Russell King <rmk+kernel@armlinux.org.uk>
Cc: Rajendra Nayak <rnayak@codeaurora.org>,
	Paul Walmsley <paul@pwsan.com>,
	linux-omap@vger.kernel.org, Will Deacon <will.deacon@arm.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2] ARM: avoid Cortex-A9 livelock on tight dmb loops
Date: Fri, 25 Jan 2019 15:20:20 -0800	[thread overview]
Message-ID: <20190125232020.GX5720@atomide.com> (raw)
In-Reply-To: <E1gn8dp-0004Ai-AW@rmk-PC.armlinux.org.uk>

* Russell King <rmk+kernel@armlinux.org.uk> [190125 21:04]:
> Executing loops such as:
> 
> 	while (1)
> 		cpu_relax();
> 
> with interrupts disabled results in a livelock of the entire system,
> as other CPUs are prevented making progress.  This is most noticable
> as a failure of crashdump kexec, which stops just after issuing:
> 
> 	Loading crashdump kernel...
> 
> to the system console.  A workaround for this is to use 10 nops in
> cpu_relax().
> 
> We also use wfe() in while (1) loops to avoid burning cycles in a
> tight loop, giving the CPU a hint that we're not doing anything
> useful.
> 
> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
> ---
> It's been a while since this was posted, Will's suggestion was to use
> 10 nops in cpu_relax() last time around.  I still prefer wfe() in
> these infinite-not-doing-anything-ever loops.

Works for me:

Tested-by: Tony Lindgren <tony@atomide.com>

WARNING: multiple messages have this Message-ID (diff)
From: Tony Lindgren <tony@atomide.com>
To: Russell King <rmk+kernel@armlinux.org.uk>
Cc: Rajendra Nayak <rnayak@codeaurora.org>,
	Paul Walmsley <paul@pwsan.com>,
	linux-omap@vger.kernel.org, Will Deacon <will.deacon@arm.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2] ARM: avoid Cortex-A9 livelock on tight dmb loops
Date: Fri, 25 Jan 2019 15:20:20 -0800	[thread overview]
Message-ID: <20190125232020.GX5720@atomide.com> (raw)
In-Reply-To: <E1gn8dp-0004Ai-AW@rmk-PC.armlinux.org.uk>

* Russell King <rmk+kernel@armlinux.org.uk> [190125 21:04]:
> Executing loops such as:
> 
> 	while (1)
> 		cpu_relax();
> 
> with interrupts disabled results in a livelock of the entire system,
> as other CPUs are prevented making progress.  This is most noticable
> as a failure of crashdump kexec, which stops just after issuing:
> 
> 	Loading crashdump kernel...
> 
> to the system console.  A workaround for this is to use 10 nops in
> cpu_relax().
> 
> We also use wfe() in while (1) loops to avoid burning cycles in a
> tight loop, giving the CPU a hint that we're not doing anything
> useful.
> 
> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
> ---
> It's been a while since this was posted, Will's suggestion was to use
> 10 nops in cpu_relax() last time around.  I still prefer wfe() in
> these infinite-not-doing-anything-ever loops.

Works for me:

Tested-by: Tony Lindgren <tony@atomide.com>

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  reply	other threads:[~2019-01-25 23:20 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-25 21:03 [PATCH v2] ARM: avoid Cortex-A9 livelock on tight dmb loops Russell King
2019-01-25 21:03 ` Russell King
2019-01-25 23:20 ` Tony Lindgren [this message]
2019-01-25 23:20   ` Tony Lindgren
2019-01-26 21:00   ` Paul Walmsley
2019-01-26 21:00     ` Paul Walmsley
2019-01-26 23:51     ` Russell King - ARM Linux admin
2019-01-26 23:51       ` Russell King - ARM Linux admin
2019-01-27  1:15       ` Paul Walmsley
2019-01-27  1:15         ` Paul Walmsley
2019-01-27 15:28         ` Russell King - ARM Linux admin
2019-01-27 15:28           ` Russell King - ARM Linux admin
2019-01-31 13:58           ` Will Deacon
2019-01-31 13:58             ` Will Deacon
2019-01-31 22:58             ` Russell King - ARM Linux admin
2019-01-31 22:58               ` Russell King - ARM Linux admin
2019-02-01 10:19 ` Will Deacon
2019-02-01 10:19   ` Will Deacon
2019-02-01 21:20   ` Russell King - ARM Linux admin
2019-02-01 21:20     ` Russell King - ARM Linux admin
  -- strict thread matches above, loose matches on Subject: below --
2018-06-01 11:00 Russell King
2018-06-01 11:00 ` Russell King
2018-06-01 15:35 ` Tony Lindgren
2018-06-01 15:35   ` Tony Lindgren
2018-06-01 15:55   ` Russell King - ARM Linux
2018-06-01 15:55     ` Russell King - ARM Linux
2018-06-01 16:12     ` Tony Lindgren
2018-06-01 16:12       ` Tony Lindgren
2018-06-04  9:42 ` Will Deacon
2018-06-04  9:42   ` Will Deacon
2018-06-04 18:08   ` Russell King - ARM Linux
2018-06-04 18:08     ` Russell King - ARM Linux

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