From: Will Deacon <will@kernel.org>
To: Robin Murphy <robin.murphy@arm.com>
Cc: mark.rutland@arm.com, tuanphan@os.amperecomputing.com,
john.garry@huawei.com, linux-kernel@vger.kernel.org,
shameerali.kolothum.thodi@huawei.com, harb@amperecomputing.com,
linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC PATCH] perf/smmuv3: Fix shared interrupt handling
Date: Wed, 24 Jun 2020 13:50:46 +0100 [thread overview]
Message-ID: <20200624125045.GC6270@willie-the-truck> (raw)
In-Reply-To: <b7d056f7-3a3d-568d-ea6d-24bb30b4761b@arm.com>
On Wed, Jun 24, 2020 at 12:48:14PM +0100, Robin Murphy wrote:
> On 2020-04-08 17:49, Robin Murphy wrote:
> > IRQF_SHARED is dangerous, since it allows other agents to retarget the
> > IRQ's affinity without migrating PMU contexts to match, breaking the way
> > in which perf manages mutual exclusion for accessing events. Although
> > this means it's not realistically possible to support PMU IRQs being
> > shared with other drivers, we *can* handle sharing between multiple PMU
> > instances with some explicit affinity bookkeeping and manual interrupt
> > multiplexing.
> >
> > RCU helps us handle interrupts efficiently without having to worry about
> > fine-grained locking for relatively-theoretical race conditions with the
> > probe/remove/CPU hotplug slow paths. The resulting machinery ends up
> > looking largely generic, so it should be feasible to factor out with a
> > "system PMU" base class for similar multi-instance drivers.
> >
> > Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> > ---
> >
> > RFC because I don't have the means to test it, and if the general
> > approach passes muster then I'd want to tackle the aforementioned
> > factoring-out before merging anything anyway.
>
> Any comments on whether it's worth pursuing this?
Sorry, I don't really get the problem that it's solving. Is there a crash
log somewhere I can look at? If all the users of the IRQ are managed by
this driver, why is IRQF_SHARED dangerous?
Will
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next prev parent reply other threads:[~2020-06-24 12:52 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-08 16:49 [RFC PATCH] perf/smmuv3: Fix shared interrupt handling Robin Murphy
2020-04-09 7:02 ` John Garry
2020-04-09 9:54 ` Robin Murphy
2020-04-30 22:11 ` Tuan Phan
2020-06-24 11:48 ` Robin Murphy
2020-06-24 12:50 ` Will Deacon [this message]
2020-06-24 13:08 ` Robin Murphy
2020-07-03 13:42 ` Will Deacon
2020-07-03 14:42 ` Robin Murphy
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