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From: Peter Zijlstra <peterz@infradead.org>
To: James Morse <james.morse@arm.com>
Cc: Waiman Long <longman@redhat.com>,
	Zhenzhong Duan <zhenzhong.duan@oracle.com>,
	LKML <linux-kernel@vger.kernel.org>,
	SRINIVAS <srinivas.eeda@oracle.com>
Subject: Re: Question about qspinlock nest
Date: Thu, 10 Jan 2019 21:12:17 +0100	[thread overview]
Message-ID: <20190110201217.GH2861@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <d06126a1-1db8-f937-2084-2c1234b6f56f@arm.com>

On Thu, Jan 10, 2019 at 06:25:57PM +0000, James Morse wrote:

> On arm64 if all the RAS and psuedo-NMI patches land, our worst-case interleaving
> jumps to at least 7. The culprit is APEI using spinlocks to protect fixmap slots.
> 
> I have an RFC to bump the number of node bits from 2 to 3, but as this is APEI
> four times, it may be preferable to make it use something other than spinlocks.
> 
> 
> The worst-case order is below. Each one masks those before it:
> 1. process context
> 2. soft-irq
> 3. hard-irq
> 4. psuedo-nmi [0]
>    - using the irqchip priorities to configure some IRQs as NMI.
> 5. SError [1]
>    - a bit like an asynchronous MCE. ACPI allows this to convey CPER records,
>      requiring an APEI call.
> 6&7. SDEI [2]
>      - a firmware triggered software interrupt, only its two of them, either of
>        which could convey CPER records.
> 8. Synchronous external abort
>    - again, similar to MCE. There are systems using this with APEI.

The thing is, everything non-maskable (NMI like) really should not be
using spinlocks at all.

I otherwise have no clue about wth APEI is, but it sounds like horrible
crap ;-)

  parent reply	other threads:[~2019-01-10 20:12 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-10  8:02 Question about qspinlock nest Zhenzhong Duan
2019-01-10 14:43 ` Waiman Long
2019-01-10 18:25   ` James Morse
2019-01-10 19:23     ` Waiman Long
2019-01-10 20:12     ` Peter Zijlstra [this message]
2019-01-11 18:32       ` James Morse
2019-01-14 13:16         ` Peter Zijlstra
2019-01-14 13:54           ` James Morse
2019-01-14 21:07             ` Waiman Long
2019-01-18 10:02             ` Peter Zijlstra
2019-01-18 10:24               ` Borislav Petkov
2019-01-18 14:50               ` Waiman Long
2019-01-18 20:06                 ` Peter Zijlstra
2019-01-18 21:30                   ` Waiman Long
     [not found]   ` <2eca6f60-3e8b-a389-27cb-8adbd9676607@oracle.com>
2019-01-11  9:16     ` Peter Zijlstra
2019-01-11 17:36       ` Borislav Petkov
2019-01-11 16:59     ` Waiman Long
2019-01-10 20:03 ` Peter Zijlstra
2019-01-14  9:25 Zhenzhong Duan

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