From: catalin.marinas@arm.com (Catalin Marinas)
To: linux-arm-kernel@lists.infradead.org
Subject: [BUG] "sched: Remove rq->lock from the first half of ttwu()" locks up on ARM
Date: Thu, 26 May 2011 15:45:39 +0100 [thread overview]
Message-ID: <BANLkTinUZ7EwN_nBCi_RQ9u8-LBcr_A74g@mail.gmail.com> (raw)
In-Reply-To: <20110526125007.GA27083@elte.hu>
On 26 May 2011 13:50, Ingo Molnar <mingo@elte.hu> wrote:
> * Russell King - ARM Linux <linux@arm.linux.org.uk> wrote:
>
>> On Thu, May 26, 2011 at 02:26:23PM +0200, Ingo Molnar wrote:
>> >
>> > * Peter Zijlstra <peterz@infradead.org> wrote:
>> >
>> > > Sort this by reverting to the old behaviour for this situation
>> > > and perform a full remote wake-up.
>> >
>> > Btw., ARM should consider switching most of its subarchitectures
>> > to !__ARCH_WANT_INTERRUPTS_ON_CTXSW - enabling irqs during
>> > context switches is silly and now expensive as well.
>>
>> Not going to happen. ?The reason we do it is because most of the
>> CPUs have to (slowly) flush their caches during switch_mm(), and to
>> have IRQs off over the cache flush means that we lose IRQs.
>
> How much time does that take on contemporary ARM hardware, typically
> (and worst-case)?
On newer ARMv6 and ARMv7 hardware, we no longer flush the caches at
context switch as we got VIPT (or PIPT-like) caches.
But modern ARM processors use something called ASID to tag the TLB
entries and we are limited to 256. The switch_mm() code checks for
whether we ran out of them to restart the counting. This ASID
roll-over event needs to be broadcast to the other CPUs and issuing
IPIs with the IRQs disabled isn't always safe. Of course, we could
briefly re-enable them at the ASID roll-over time but I'm not sure
what the expectations of the code calling switch_mm() are.
--
Catalin
next prev parent reply other threads:[~2011-05-26 14:45 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-24 18:13 [BUG] "sched: Remove rq->lock from the first half of ttwu()" locks up on ARM Marc Zyngier
2011-05-24 21:32 ` Peter Zijlstra
2011-05-24 21:39 ` Ingo Molnar
2011-05-25 12:23 ` Marc Zyngier
2011-05-25 17:08 ` Peter Zijlstra
2011-05-25 21:15 ` Peter Zijlstra
2011-05-26 7:29 ` Yong Zhang
2011-05-26 10:32 ` Peter Zijlstra
2011-05-26 11:02 ` Marc Zyngier
2011-05-26 11:32 ` Peter Zijlstra
2011-05-26 12:21 ` Peter Zijlstra
2011-05-26 12:26 ` Ingo Molnar
2011-05-26 12:31 ` Russell King - ARM Linux
2011-05-26 12:37 ` Peter Zijlstra
2011-05-26 12:50 ` Ingo Molnar
2011-05-26 13:36 ` Russell King - ARM Linux
2011-05-26 14:45 ` Catalin Marinas [this message]
2011-05-27 12:06 ` Ingo Molnar
2011-05-27 17:55 ` Russell King - ARM Linux
2011-05-27 19:41 ` Nicolas Pitre
2011-05-27 20:52 ` Russell King - ARM Linux
2011-05-28 13:13 ` Peter Zijlstra
2011-05-31 11:08 ` Michal Simek
2011-05-31 13:22 ` Peter Zijlstra
2011-05-31 13:37 ` Michal Simek
2011-05-31 13:52 ` Peter Zijlstra
2011-05-31 14:08 ` Michal Simek
2011-05-31 14:29 ` Peter Zijlstra
2011-05-29 10:21 ` Catalin Marinas
2011-05-29 10:26 ` Russell King - ARM Linux
2011-05-29 12:01 ` Catalin Marinas
2011-05-29 13:19 ` Russell King - ARM Linux
2011-05-29 21:21 ` Catalin Marinas
2011-05-29 9:51 ` Catalin Marinas
2011-06-06 10:29 ` Pavel Machek
2011-05-26 14:56 ` Marc Zyngier
2011-05-26 15:45 ` Oleg Nesterov
2011-05-26 15:59 ` Peter Zijlstra
2011-05-26 16:09 ` Peter Zijlstra
2011-05-26 16:20 ` Marc Zyngier
2011-05-26 16:32 ` Peter Zijlstra
2011-05-27 8:01 ` Marc Zyngier
2011-05-26 16:22 ` Marc Zyngier
2011-05-26 17:04 ` Oleg Nesterov
2011-05-26 17:17 ` Peter Zijlstra
2011-05-26 17:23 ` Peter Zijlstra
2011-05-26 17:49 ` Oleg Nesterov
2011-05-27 7:01 ` Yong Zhang
2011-05-27 15:23 ` Santosh Shilimkar
2011-05-27 15:29 ` Marc Zyngier
2011-05-27 15:30 ` Santosh Shilimkar
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