netdev - Re: Extend irq_set_affinity_notifier() to use a call chain

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Message-ID: <5384498A.9080900@mellanox.com>
Date:	Tue, 27 May 2014 11:15:06 +0300
From:	Amir Vadai <amirv@...lanox.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Ben Hutchings <ben@...adent.org.uk>,
	"David S. Miller" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Or Gerlitz <ogerlitz@...lanox.com>, <idos@...lanox.com>,
	Yevgeny Petrilin <yevgenyp@...lanox.com>
Subject: Re: Extend irq_set_affinity_notifier() to use a call chain

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

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