From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Gunthorpe Subject: Re: [PATCH for-next V2 0/9] Add completion timestamping support Date: Wed, 3 Jun 2015 22:25:40 -0600 Message-ID: <20150604042540.GA8837@obsidianresearch.com> References: <1433074457-26437-1-git-send-email-ogerlitz@mellanox.com> <1433098827.114391.179.camel@redhat.com> <1433157904.114391.188.camel@redhat.com> <20150601164322.GA14391@obsidianresearch.com> <1433255724.114391.225.camel@redhat.com> <20150602180844.GD17776@obsidianresearch.com> <20150603204633.GE7902@obsidianresearch.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Christoph Lameter Cc: Or Gerlitz , Doug Ledford , Matan Barak , Or Gerlitz , "linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Amir Vadai , Tal Alon List-Id: linux-rdma@vger.kernel.org On Wed, Jun 03, 2015 at 07:55:58PM -0500, Christoph Lameter wrote: > I thknk the raw cycles and the rought oscillator speed are fine. Time keeping is designed to adjust for 100's of ppm drift between clocks. A communications clock source will be spec'd to be below 200ppm in accuracy. IB clocks are below 100 ppm, and PCI-E is 300ppm (approx, I didn't check, order of magnitue is close) That translates into 0.0625 Hz. for a 312.5 MHz ethernet reference clock Compared to 5,000,000 Hz in error from rounding. So no, I disagree that rough is fine for anything. Jason -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html