Anyone fancy a free performance upgrade? Well if you are running a POWER8 or POWER9 and your firmware is up to date, you may just be able to get a performance increase by changing a single setting in the Hypervisor. This is not an April Fool, it a free 10% performance boost that is free of charge. That’s right free, gratis, zip, nada, buckshee, not a penny, not a sausage!
Where has this come from you might ask? Well, some of you might remember my article from February last year “Don’t have a Meltdown over Spectre” (https://powerwire.wpengine.com/dont-have-a-meltdown-over-spectre) where we discussed a theoretical vulnerability in modern processor architecture. As you would expect, IBM promptly addressed the issue in POWER8 servers with firmware update and the POWER9 servers were protected from the outset.
We are now some 18 months on from the first reports of the risks of Speculative Execution vulnerabilities such as those outlined in CVE-2017-5753, CVE-2017-5754 and CVE-2017- 5715 and here is the irony:
Speculation is all we have seen. No real world uses of this sort of threat have surfaced, NOT ONE. And as discussed in the article, even if they did it would only pose a threat if you shared your POWER hardware with LPARs that were out of your control.
IBM has handled this in a remarkably sensible and responsible way, they have of course set our servers to be protected by default from Speculative Execution attacks but they have given you the option to disable this protection where it is felt to be unnecessary, and so benefit from the resulting boost in performance.
So, assuming you don’t run on a shared system and that your system is eligible, I would recommend you consider getting the latest firmware loaded on your POWER8 or POWER9 server, scheduling a brief period of down time where you can shut down to make the following change:
Open the ASMI (Advanced System Management Interface), login in as the admin user and navigate to > System Configuration > Speculative Execution Control.
Once there, you can set your system to “Speculative execution fully enabled”, save the changes and of course to keep IBM legal happy, click the “Are you sure you want to do this” dialogue.
That’s it, just start the server back up again as normal and enjoy your free performance boost.
IBM’s official guidance can be found at the link below, it’s brief and to the point and well worth a read before you make the change on your system: https://www.ibm.com/support/knowledgecenter/POWER9/p9hby/p9hby_speculative_execution_control_914_922_924.htm
Your mileage may vary
IBM has not published any official figures for the improvement in performance that this change will yield but they did publish the rPERF and CPW values for POWER8 systems both with and without Speculative Execution Protection enabled, and on a typical POWER8 system there was approximately a 10% difference.
So of course, I have to throw out the standard disclaimers that:
This is a decision you have to consider and make on your own.
And, that your performance gain may vary.
But for the vast majority of IBM i customers out there, I feel this is a no brainer and let’s face it, if you change your mind, you can change it back just as easily.
Nice to see you
It was great to see you all in Rochdale and London, the atmosphere was amazing.
I’m delighted to say that we are now working on the i-UG’s largest ever event at Milton Keynes on 11h & 12th June.
More details and registration button are available at our website https://www.i-ug.co.uk/international-i-power-2019