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From: Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
To: "Weiny, Ira" <ira.weiny-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Cc: Alex Rosenbaum
	<rosenbaumalex-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	"linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"leon-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org"
	<leon-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Yishai Hadas <yishaih-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Subject: Re: [RFC] libibverbs IB device hotplug support
Date: Wed, 1 Mar 2017 16:07:43 -0700	[thread overview]
Message-ID: <20170301230743.GC2820@obsidianresearch.com> (raw)
In-Reply-To: <2807E5FD2F6FDA4886F6618EAC48510E67C5CA68-8k97q/ur5Z2krb+BlOpmy7fspsVTdybXVpNB7YpNyf8@public.gmane.org>

On Wed, Mar 01, 2017 at 10:15:31PM +0000, Weiny, Ira wrote:
> > On the call we discussed that today there is no 'incarnation'
> > value exposed for the uverbs%.  You suggested an optimization by
> > using the cdev's file creation timestamp as option for libibverbs
> > to understand that the driver did or did-not restart since mapping
> > of that ibv_device.

Not the cdev, read the timestamp from /sys/class/infiniband/mlx4_0/hca_type

> > Main pitfalls with this is if system time is being modified (admin
> > or ntp/ptp). In the rare case that we have a hoplug event and time
> > is rewinded we can accidentally reach a very hard debugging
> > exercise.

You are only using it for direct equality comparision, so someone
would have to roll back the clock and hotplug the driver at the exact
same nano-second resolution timestamp. That is deeply unlikely to ever
happen by accident.

Jason
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  parent reply	other threads:[~2017-03-01 23:07 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-02-27 16:08 [RFC] libibverbs IB device hotplug support Alex Rosenbaum
     [not found] ` <CAFgAxU9eQYwBad2+SJw1x+cQMMqzgkz0fpeumG7Rx=o_eQqo2g-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-02-27 18:59   ` Jason Gunthorpe
     [not found]     ` <20170227185912.GM5891-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
2017-02-27 22:11       ` Alex Rosenbaum
     [not found]         ` <CAFgAxU9XJTXkaeL_VE7zHASPBM+j=TZd2L+McKBcJRThJtUN5w-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-02-27 22:36           ` Jason Gunthorpe
     [not found]             ` <20170227223600.GA1526-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
2017-02-28  7:56               ` Alex Rosenbaum
     [not found]                 ` <CAFgAxU8KkrOS6aib4ykf8vj1sQFGK_oMW=fX3vZ2X2_r3ryDVA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-02-28 21:26                   ` Jason Gunthorpe
2017-02-28 15:48   ` Doug Ledford
     [not found]     ` <1488296882.86943.214.camel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2017-02-28 16:32       ` Liran Liss
     [not found]         ` <HE1PR0501MB28123E8F342607E2C2CA4DD9B1560-692Kmc8YnlIVrnpjwTCbp8DSnupUy6xnnBOFsp37pqbUKgpGm//BTAC/G2K4zDHf@public.gmane.org>
2017-02-28 21:47           ` Doug Ledford
     [not found]             ` <3389d831-c135-b326-4b96-5f2a746de5ac-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2017-03-01  0:44               ` Jason Gunthorpe
     [not found]                 ` <20170301004449.GA13114-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
2017-03-01 18:00                   ` Hefty, Sean
     [not found]                     ` <1828884A29C6694DAF28B7E6B8A82373AB0ECDC6-P5GAC/sN6hkd3b2yrw5b5LfspsVTdybXVpNB7YpNyf8@public.gmane.org>
2017-03-01 18:07                       ` Jason Gunthorpe
2017-03-01 21:47                       ` Alex Rosenbaum
     [not found]                         ` <CAFgAxU9vObaW4O+byEJ5pV1Ofou4cd05HHWWPC7iTJshyk+LdA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-03-01 22:07                           ` Doug Ledford
     [not found]                             ` <d92df6b7-207f-f3a3-8bf5-b12cffe20684-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2017-03-01 22:32                               ` Alex Rosenbaum
     [not found]                                 ` <CAFgAxU_-jbAoOR2XMYfSgbDMn7FnrthudZJLgeNNTzb9GEUXrg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-03-02 12:48                                   ` Doug Ledford
     [not found]                                     ` <467c0560-8de7-42e5-14b9-178c367874d2-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2017-03-02 16:53                                       ` Jason Gunthorpe
2017-03-01 23:18                           ` Hefty, Sean
2017-03-01 21:56                       ` Doug Ledford
     [not found]                         ` <cad3d2c6-0c98-9f58-a3bb-81823103bd76-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2017-03-01 22:23                           ` Jason Gunthorpe
2017-03-01 22:34                           ` Alex Rosenbaum
2017-03-01  0:10   ` ira.weiny
     [not found]     ` <20170301001023.GA3001-W4f6Xiosr+yv7QzWx2u06xL4W9x8LtSr@public.gmane.org>
2017-03-01 21:21       ` Alex Rosenbaum
     [not found]         ` <CAFgAxU-Vf6RLEo8N=oya0X+WbneRHE1xa_-5GY+TEqo1wyzpow-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-03-01 22:17           ` Weiny, Ira
     [not found]             ` <2807E5FD2F6FDA4886F6618EAC48510E67C5CA80-8k97q/ur5Z2krb+BlOpmy7fspsVTdybXVpNB7YpNyf8@public.gmane.org>
2017-03-01 22:38               ` Alex Rosenbaum
2017-03-01 21:57       ` Alex Rosenbaum
     [not found]         ` <CAFgAxU_i+5FtBkdf=t5vdQAvBqDt9aKsFJbAKGN5YWQQ9w-c2A-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-03-01 22:15           ` Weiny, Ira
     [not found]             ` <2807E5FD2F6FDA4886F6618EAC48510E67C5CA68-8k97q/ur5Z2krb+BlOpmy7fspsVTdybXVpNB7YpNyf8@public.gmane.org>
2017-03-01 22:42               ` Alex Rosenbaum
2017-03-01 23:07               ` Jason Gunthorpe [this message]
     [not found]                 ` <20170301230743.GC2820-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
2017-03-02 13:22                   ` Leon Romanovsky
2017-03-02 16:08   ` Hefty, Sean
     [not found]     ` <1828884A29C6694DAF28B7E6B8A82373AB0ED3C6-P5GAC/sN6hkd3b2yrw5b5LfspsVTdybXVpNB7YpNyf8@public.gmane.org>
2017-03-03 12:31       ` Alex Rosenbaum

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