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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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  parent reply	other threads:[~2018-04-20  3:56 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-18 14:24 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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