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From: Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
Subject: Re: [PATCH for-next 09/10] IB/mlx4: Add timestamp_mask and
 hca_core_clock to query_device
Date: Thu, 28 May 2015 11:50:43 -0600
Message-ID: <20150528175043.GA10966@obsidianresearch.com>
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To: Christoph Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>
Cc: Or Gerlitz <ogerlitz-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>, Doug Ledford <dledford-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, "linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Amir Vadai <amirv-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>, Tal Alon <talal-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>, Matan Barak <matanb-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>, Yann Droneaud <ydroneaud-RlY5vtjFyJ3QT0dZR+AlfA@public.gmane.org>
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On Thu, May 28, 2015 at 12:14:15PM -0500, Christoph Lameter wrote:
> On Thu, 28 May 2015, Jason Gunthorpe wrote:
> 
> > After a quick look through, the biggest question in my mind is what
> > should the timestamp value in the wc be?
> >
> > Right now it is some coded thing in clock cycles.
> 
> This is sufficient since it can be converted to ns or whatever one wants.

Sure it is sufficient, but is it a robust UAPI, will it support
multiple hardware vendors?

Is anyone else in ethernet using verbs to deliver IP packets?

Having a conversion function, or doing it in the wc generation is more
'obviously safe' for future proofing the UAPI.

> > Should we require the driver to convert to ns before passing the wc
> > back to the app? (Looks like the socket implementation uniformly uses
> > us or ns)

> But that requires additional processing.

Well, it is only additional if the app is going to ignore the time
stamp or not convert it to ns right away. Is that the common use case?

Jason
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