On 2016/06/15 16:51:38 -0700, Paul E. McKenney wrote: > On Sat, Jun 11, 2016 at 03:39:31PM +0900, Akira Yokosawa wrote: >> >From 1ff97081c713ff51d5bc2e15f8ba7649427fac4f Mon Sep 17 00:00:00 2001 >> From: Akira Yokosawa <akiyks@xxxxxxxxx> >> Date: Sat, 11 Jun 2016 15:28:20 +0900 >> Subject: [PATCH] cpu: Fix numbers in Performance of Mechanisms table in qqz >> >> Numbers given in 'Comms Fabric' and 'Global Comms' rows in >> Table D.1 seem wrong. >> >> Their costs are given in ns unit, so they should match those given >> in Table 3.1. >> >> Also, their ratio should be calculated by cost(ns)/0.36(ns). >> >> This commit fixes those numbers. > > Great catch, but let's talk about the fix. > > The 130ms is the time required for light to circumnavigate the earth > in a vacuum. The 195ms is that for light to circumnavigate the earth > in glass, as in an optical fiber. There is some variation due to > different refractive indexes of different types of fiber. > > So making both of those entries be 195,000,000 seems like the right > approach. An even better approach would be to use the ping time to > some system on the other side of the world, but I am coming up empty. > Pinging google.com gets me 216.58.217.46 for about 47ms. If you are > far away from West Coast USA, please see what you get. Not that I > would put it past Google to spread a single IP address worldwide to > defeat this, but worth a try... > > On the Comms Fabric number, I suspect that I just googled this at > two different times and got two different numbers. Not surprising, > as different products would be optimized differently at different > times. > > So how about https://en.wikipedia.org/wiki/InfiniBand? Choose the > value in effect when Nehalem was released for the QQ table, and choose > the value in effect when the AMD Opteron 844 was released for the > table in Chapter 3. > > Seem reasonable? > > Oh, and also add a Latex comment saying where the data came from! ;-) Hi, I took some time collecting latency data, and composed v2 of the patch. Will send it in reply to this mail. Thanks, Akira > > Thanx, Paul > >> Signed-off-by: Akira Yokosawa <akiyks@xxxxxxxxx> >> --- >> cpu/overheads.tex | 8 ++++---- >> 1 file changed, 4 insertions(+), 4 deletions(-) >> >> diff --git a/cpu/overheads.tex b/cpu/overheads.tex >> index 311c43e..0cf83f3 100644 >> --- a/cpu/overheads.tex >> +++ b/cpu/overheads.tex >> @@ -224,11 +224,11 @@ global agreement. >> \hline >> CAS cache miss & 95.9 & 266.4 \\ >> \hline >> - Comms Fabric & 4,500\textcolor{white}{.0} >> - & 7,500\textcolor{white}{.0} \\ >> + Comms Fabric & 3,000\textcolor{white}{.0} >> + & 8,330\textcolor{white}{.0} \\ >> \hline >> - Global Comms & 195,000,000\textcolor{white}{.0} >> - & 324,000,000\textcolor{white}{.0} \\ >> + Global Comms & 130,000,000\textcolor{white}{.0} >> + & 361,000,000\textcolor{white}{.0} \\ >> \end{tabular} >> \caption{Performance of Synchronization Mechanisms on 16-CPU 2.8GHz Intel X5550 (Nehalem) System} >> \label{tab:cpu:Performance of Synchronization Mechanisms on 16-CPU 2.8GHz Intel X5550 (Nehalem) System} >> -- >> 1.9.1 >> > > -- To unsubscribe from this list: send the line "unsubscribe perfbook" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
