The IBM POWER8 Review: Challenging the Intel Xeon
by Johan De Gelas on November 6, 2015 8:00 AM EST- Posted in
- IT Computing
- CPUs
- Enterprise
- Enterprise CPUs
- IBM
- POWER
- POWER8
Trying Out a Different Compiler: IBM's XLC
Based on our previous results the IBM POWER8 has definitely attracted our interest, and we were motivated to test a lot more. Can IBM's own compiler "XLC" boost the scores even more?
To test that out, we joined the IBM OpenPOWER Linux community and downloaded the IBM XLC compiler. We compiled with two different and rather aggressive settings:
- -qhot -O4 -qarch=pwr8
- -qhot -O5 -qarch=pwr8
We've taken our XLC binaries and set them up against binaries compiled with GCC 4.9.2 using the "-o3 -mcpu=power8" flag. The mcpu=power8 flag has very little impact on performance, but we wanted to be sure that GCC was given every opportunity to optimize for the POWER8 CPU.
The results for XLC are very weird. Using the -O4 flag the XLC compiler does pretty badly on compression (-7%), while increasing performance by 7% in decompression. Nothing to write home about. Only when we use the -O5 flag do we get an increase in performance by 7-8%. However we also found that -O5 was too aggressive for most complex software that we ported to the POWER8, and as a result isn't very usable.
We suspect that the XLC compiler for LE Linux is still a bit immature and has still some room to improve. Which unfortunately isn't doing IBM any favors at this moment since XLC is a paid compiler.
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joegee - Thursday, November 19, 2015 - link
It was an awesome community. I learned so much from everyone. I remember the days when we'd write pages arguing whether AMD's new 64 bit extension to x86 was truly 64 bit. The discussions could be heated, but they were seldom rude. I wish there were something similar today. :/Kevin G - Saturday, November 7, 2015 - link
Aces brings back memories for me as well even though I mainly lurked there.A solid chunk of that group have moved over to RWT.
joegee - Thursday, November 19, 2015 - link
What is RWT?psychobriggsy - Friday, November 6, 2015 - link
Get back to Aces Hardware you!JohanAnandtech - Saturday, November 7, 2015 - link
Like Ryan said, I have been working 11 years at Anand. In other words, it is great working at Anandtech. AT is one of the few tech sites out there that still values deep analysis and allows the editors to take the time to delve deep.joegee - Friday, November 6, 2015 - link
And still writing as well as you ever did! Keep up the good work, Johan!rrossi - Saturday, November 7, 2015 - link
Dear Johan nice article. Did u ever consider sparse system solving (with preconditioning) as a sensitive benchmark? It is a crucial stage of most scientific applications and it is a bandwidth limited operation with a high degree of parallelism. It would be definitely interesting to see how the power 8 fares on such a test. If you are interested I think I could provide a pointer to a simple benchmark (to be compiled). If you feel it may be interesting just drop me an email.JohanAnandtech - Saturday, November 7, 2015 - link
Interested... mail me, I don't have your mail. See the author link on top of the article.Ian Cutress - Saturday, November 7, 2015 - link
I'd also like to be pointed to such a benchmark for workstation style tests on x86. Please email ian@anandtech.com with info :)MartinT - Friday, November 6, 2015 - link
Johan's been with Anandtech for more than a decade, and has been publishing on the subject since the late 90s.But I very much second your "Niiiiice!," as reading his name always reminds me of the old days over at aceshardware, and I'm always looking forward to his insights!