Stan Hoeppner wrote: > Bob Proulx put forth: > > Here is some raw data from another test using GraphicsMagic from Debian > > Sid on an Intel Core2 Quad CPU Q9400 @ 2.66GHz. > > > > #CPUs real user sys > > 1 ... 32.17 100.15 2.29 > > 2 ... 28.02 102.09 2.25 > > 3 ... 26.96 101.41 2.02 > > 4 ... 26.18 99.85 2.10 > > 5 ... 26.03 98.58 2.27 > > 6 ... 27.07 97.32 2.17 > > 7 ... 27.74 100.09 2.03 > > 8 ... 26.76 97.83 1.99 > > 9 ... 27.24 97.31 2.88 > > 10 ... 26.27 99.05 2.76 > > 11 ... 26.35 99.30 1.84 > > 12 ... 25.91 97.63 2.08 > > So, I'm not understanding how we have a quad core CPU with 12 CPUs. > Is "#CPUs" here your xargs "-P" argument in the script you posted in > response to my question that started this thread?
Sorry. Yes I made a mistake in posting those headings. Yes it was the xargs -P parallelization argument listed where I said #CPUs. Running a different number of conversion processes in parallel. > Why bother going up to 12 processes with a quad core chip? Anything > over 4 processes/threads won't gain you anything, as your results > above demonstrate. I went to 12 because it would demonstrate the behavior three times past the number of cores. If I had only a dual core I would have only chosen to go to 6. But I would have gone to 6 for one core too since three doesn't generate a smooth enough scatter plot for me. But I didn't want to spend too much time analyzing the problem to set up a statistically designed experiment. I just wanted to quickly perform the test. So plucked in 12 there and moved on. Surely that would be enough. I didn't think I would need to rigorously defend that quick choice against a panel. At some point by doing more parallelism things will actually be slowed down by it. I didn't reach that point. > > And the same thing using ImageMagick on the same system. > > > > #CPUs real user sys > > 1 ... 24.69 62.60 2.87 > > 2 ... 19.28 63.17 2.50 > > 3 ... 17.82 60.34 2.65 > > 4 ... 17.48 58.86 2.55 > > 5 ... 16.60 58.11 2.34 > > 6 ... 15.85 58.03 2.38 > > 7 ... 15.61 58.09 2.44 > > 8 ... 15.36 57.68 2.48 > > 9 ... 15.48 57.76 2.38 > > 10 ... 15.38 57.76 2.28 > > 11 ... 15.36 57.97 2.27 > > 12 ... 15.73 58.76 2.17 > > > > Watching the individual cpu load I observe that while the 1 cpu case > > did consume one cpu fully that the other three were also showing quite > > a bit of activity too. > > Imagemagick will use threads on larger images. To keep it from threading, in > order for your testing to make more sense, use smaller images. I couldn't find anything in the ImageMagick documentation that described its threading behavior. Where did I miss that useful information? For images I used your set of "benchmark" photos that we have been discussing in this thread. > > three running all four cpus were looking pretty much 100% consumed. I > > was timing all of the shell's for loop, the xargs and the convert > > processes all together. > > If you are converting images large enough that the threading kicks > in, there's little reason to use multiple processes at that point. > We'd already discussed this. Were you simply trying to confirm that > with these tests? I expected that on this machine that the memory backplane wouldn't have enough memory bandwidth to support all four processors. I expect it to brown out before getting to four. Having a quad-core sounds great but just having four cores doesn't mean all of them can be used at the same time to advantage. I expect that the "extra" cores will get starved. And so the curve will drop off sooner than four. > > I also tried running this same test on some slower hardware. I have > > gotten spoiled by the faster machine. The benchmark is still running > > on my slower machines. :-) I am not going to wait for it to finish. > > What are the CPU specs of this older machine? I tested this on an Intel Celeron 2.4GHz machine with 2.5G ram. Unfortunately I see now that I have lost the saved data from that test. (Drat! I know what I did but I would need to run the test again to regenerate.) But an entire run to six parallel conversions there as I recall took over thirty minutes of total time to complete and as I recall worked out to being twenty times slower. Don't hold me to those numbers as I would need to capture the actual data again to be sure and I don't want to spend the time to do that. But it was slower, much slower. (This is actually my main web server and normally does image conversions when I upload photos. This information is probably going to motivate me to set up a task queue to speed up my image conversions there.) Bob
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