Re: [PATCH] kmod: Run usermodehelpers only on cpus allowed forkthreadd V2

[Christoph Lameter]

On Thu, 7 Nov 2013, Frederic Weisbecker wrote:

> usermodehelper works are created via workqueues, right? And workqueues are an issue as
> well for those who want CPU isolation.

AFAICT usermodehelper can be called from a variety of contexts.

> So this looks like a more general problem than just call_usermodehelper.

Well the code explicitly sets the the affinity mask to all cpus which
creates a problem for low latency processors. It does not inherit the
affinity from any calling process.

> Last time I checked, it seemed to me that this is an unbound workqueue? If so can't we tune
> the affinity of this workqueue? If not perhaps that's something we want to solve and which
> could be useful for all the users who don't want their CPU to be disturbed.

There are various contexts from which usermodehelper can be called.
Drivers use it etc.
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