topic I can't point to a positive in Software Tuning, Performance Optimization & Platform Monitoring

CPU supports clwb and clflushopt

kai_w_ — Mon, 13 Feb 2017 08:45:42 GMT

Hi all, I'm trying to find an Intel CPU which supports clwb and clflushopt. Can anyone give me some information about it? Thanks.

I can't point to a positive

McCalpinJohn — Mon, 13 Feb 2017 17:23:29 GMT

I can't point to a positive result, but I see negative results on Xeon E5 v1 (Sandy Bridge EP), Xeon E5 v2 (Ivy Bridge EP), Xeon E5 v3 (Haswell EP), Xeon E5 v4 (Broadwell EP), Atom C2xxx, Xeon Phi (Knights Corner), and Xeon Phi x200 (Knights Landing).

I don't have any Skylake client platforms to test -- that seems like the most likely place for these instructions to first show up....

CLFlushOpt and CLWB is meant

Adrian_C_ — Sat, 11 Mar 2017 05:59:47 GMT

CLFlushOpt and CLWB is meant for use with non-volatile memory. I would expect it to come out with products that support the new Optane technology. http://www.intel.com/content/www/us/en/architecture-and-technology/intel-optane-technology.html

Just for clarification: The

Thomas_W_Intel — Fri, 24 Mar 2017 13:17:52 GMT

Just for clarification: The Optane drives that launched earlier this week are implementing block I/O (over NVMe). There is the option to use Intel Memory Drive Technology, which adds a software layer to expose the drives memory as system memory. CLFLUSHOPT won't be needed for that.

On the other hand, CLFLUSHOPT could be useful for other use-cases than non-volatile memory. In fact, CLFLUSHOPT comes close to the original description of CLFLUSH. However, the instruction set reference manual has now been updated with the information that CLFLUSH is not only ordered in respect to MFENCE but with writes and locked read-modify-write instructions as well. (This has always been the case but was not documented in the past.)

My Intel Core i7-7500U seems to support CLFLUSHOPT but not CLWB. Unfortunately, ark.intel.com does not list this feature flag, so I'm relying on HWINFO64.