Re: [PATCH 1/4] spi: For controllers that need realtime always use the pump thread

[Mark Brown]

On Fri, May 10, 2019 at 03:34:34PM -0700, Douglas Anderson wrote:
> If a controller specifies that it needs high priority for sending
> messages we should always schedule our transfers on the thread.  If we
> don't do this we'll do the transfer in the caller's context which
> might not be very high priority.

If performance is important you probably also want to avoid the context
thrashing - executing in the calling context is generally a substantial
performance boost.  I can see this causing problems further down the
line when someone else turns up with a different requirement, perhaps in
an application where the caller does actually have a raised priority
themselves and just wanted to make sure that the thread wasn't lower
than they are.  I guess it'd be nice if we could check what priority the
calling thread has and make a decision based on that but there don't
seem to be any facilities for doing that which I can see right now.

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