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Date: Tue, 27 May 2014 11:15:06 +0300
From: Amir Vadai <amirv@mellanox.com>
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To: Thomas Gleixner <tglx@linutronix.de>
CC: Ben Hutchings <ben@decadent.org.uk>,
        "David S. Miller" <davem@davemloft.net>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Or Gerlitz <ogerlitz@mellanox.com>, <idos@mellanox.com>,
        Yevgeny Petrilin <yevgenyp@mellanox.com>
Subject: Re: Extend irq_set_affinity_notifier() to use a call chain
References: <5381DEDC.8050204@gmail.com> <alpine.DEB.2.02.1405261313570.21720@ionos.tec.linutronix.de> <53832472.7070000@gmail.com> <alpine.DEB.2.02.1405261327500.21720@ionos.tec.linutronix.de> <53832D28.1050207@mellanox.com> <alpine.DEB.2.02.1405261412110.21720@ionos.tec.linutronix.de>
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On 5/26/2014 3:39 PM, Thomas Gleixner wrote:

[...]

>
> The rmap _IS_ instantiated by the driver, and both the driver and the
> networking core know about it.
>
> So it's not completely different consumers. Just because it's a
> library does not mean it's disjunct from the code which uses it.
>
> Aside of the fact, that maintaining a per irq notifier chain is going
> to be ugly as hell due to life time and locking issues, it's just
> opening a can of worms. How do you make sure that the invocation order
> is correct? What are the dependency rules of the driver restarting the
> napi session versus updating the rmap?
>
> Even if you'd solve that and have a callback in the driver, then the
> callback never can restart the napi session directly. All it can do is
> set a flag which needs to be checked in the RX path, right?
>
> So what's the point of adding notifier call chain complexity, ordering
> problems etc., if you can simply note the fact that the affinity
> changed in the rmap itself and check that in the RX path?

I will try to find a solution in the spirit of what you suggested - to 
let the rmap library notify napi about affinity changes - without adding 
this complexity to the code.

Thanks,
Amir

>
> Thanks,
>
> 	tglx