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Message-ID: <1524196555.11756.30.camel@redhat.com>
Subject: Re: [PATCH] IB/core: Make ib_mad_client_id atomic
From:   Doug Ledford <dledford@redhat.com>
To:     =?ISO-8859-1?Q?H=E5kon?= Bugge <Haakon.Bugge@oracle.com>,
        Don Hiatt <don.hiatt@intel.com>,
        Dasaratharaman Chandramouli 
        <dasaratharaman.chandramouli@intel.com>,
        Ira Weiny <ira.weiny@intel.com>,
        Sean Hefty <sean.hefty@intel.com>
Cc:     linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org
Date:   Thu, 19 Apr 2018 23:55:55 -0400
In-Reply-To: <20180418142450.15581-1-Haakon.Bugge@oracle.com>
References: <20180418142450.15581-1-Haakon.Bugge@oracle.com>
Organization: Red Hat, Inc.
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On Wed, 2018-04-18 at 16:24 +0200, H=C3=A5kon 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.
>=20
> It is however confusing and not future robust. Hence, making it
> atomic.
>=20

People sometimes underestimate the performance penalty of atomic ops.=20
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?

--=20
Doug Ledford <dledford@redhat.com>
    GPG KeyID: B826A3330E572FDD
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