From: Doug Ledford <dledford@redhat.com>
To: "Håkon 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
Subject: Re: [PATCH] IB/core: Make ib_mad_client_id atomic
Date: Thu, 19 Apr 2018 23:55:55 -0400 [thread overview]
Message-ID: <1524196555.11756.30.camel@redhat.com> (raw)
In-Reply-To: <20180418142450.15581-1-Haakon.Bugge@oracle.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>
GPG KeyID: B826A3330E572FDD
Key fingerprint = AE6B 1BDA 122B 23B4 265B 1274 B826 A333 0E57 2FDD
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next prev parent reply other threads:[~2018-04-20 3:55 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-18 14:24 [PATCH] IB/core: Make ib_mad_client_id atomic Håkon Bugge
2018-04-18 18:51 ` Weiny, Ira
2018-04-19 2:59 ` Yanjun Zhu
2018-04-20 3:55 ` Doug Ledford [this message]
2018-04-20 15:34 ` Jason Gunthorpe
2018-04-23 14:19 ` Håkon Bugge
2018-04-23 19:16 ` jackm
2018-04-26 16:06 ` Håkon Bugge
2018-04-26 18:32 ` jackm
[not found] ` <9fdd3ec4-ee91-5442-e753-25d2ecd27ea9@xsintricity.com>
[not found] ` <A58D5192-06E7-46A3-869C-273E9A2BC128@oracle.com>
2018-04-27 19:08 ` Doug Ledford
2018-04-30 11:50 ` Håkon Bugge
2018-04-30 14:49 ` Jason Gunthorpe
2018-04-30 17:10 ` Doug Ledford
2018-04-30 17:49 ` Weiny, Ira
2018-04-30 23:01 ` Jason Gunthorpe
2018-05-01 4:38 ` jackm
2018-05-01 6:40 ` Håkon Bugge
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