Re: [PATCH] IB/core: Make ib_mad_client_id atomic

[Doug Ledford <dledford@redhat.com>]

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On Wed, 2018-04-18 at 16:24 +0200, Håkon Bugge wrote:
> Two kernel threads may get the same value for agent.hi_tid, if the
> agents are registered for different ports. As of now, this works, as
> the agent list is per port.
> 
> It is however confusing and not future robust. Hence, making it
> atomic.
> 

People sometimes underestimate the performance penalty of atomic ops. 
Every atomic op is the equivalent of a spin_lock/spin_unlock pair.  This
is why two atomics are worse than taking a spin_lock, doing what you
have to do, and releasing the spin_lock.  Is this really what you want
for a "confusing, let's make it robust" issue?

-- 
Doug Ledford <dledford@redhat.com>
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