+1 yes, pcid makes a big improvement (I've been testing the KPTI patches with and without pcid).
> I did manage to pull out an old Lenovo ThinkPad W510 with an Intel Core i7 720QM Clarksfield that is from 2009 and lacks PCID but is affected by this cpu_insecure issue.
> On that old Clarksfield-era ThinkPad I wasn't going to be surprised if the performance was disastrous, but it wound up being better than I had anticipated given all the ongoing drama... In general purpose workloads there was no reportable performance difference in our frequent benchmark test cases. Under I/O, the PTI-using kernel did yield some slower results but not by the margins seen on the newer systems with faster storage. The laptop consumer-grade HDD in this laptop appeared to be the main bottleneck and kernel inefficiencies weren't causing as dramatic slowdowns.
> To some surprise, when carrying out network benchmarks with netperf/iperf3, in at least those contexts PTI didn't have a noticeable impact on the network throughput performance.
Can anyone confirm that the way to identify if a linux system has pcid support is to check /proc/cpuinfo? Or is that merely to identify if the hw supports it, independent of the kernel support?
I checked two ubuntu servers, one 14.04, the other 16.04, both have it. Which seems odd given the claim that it's only been added recently to the kernel.
Also I see nothing showing up in dmesg, no config option and no proc interface on any system.
I saw a post in the last few days that said that most Macintoshes have this feature and Apple has been using it. Can anyone confirm that?
It seems to be a double win for bare metal machines. They always have PCID and they're less at risk in the first place since they don't share the hardware.
Virtualbox seems to lack PCID too.
This will be good to keep in mind when looking at performance reports.
The main performance numbers I've seen so far are from two kinds of sources:
1. Local benchmarks like the Phoronix benchmarks, which I think are all on physical hardware with PCID.
2. Reports from cloud customers like https://forums.aws.amazon.com/thread.jspa?threadID=269858 and https://twitter.com/chanian/status/949457156071288833. These are with a patched host, but with an unpatched guest OS. The best case scenario here seems to be that it doesn't degrade much further when the guest OS is patched.
I don't think I've seen any numbers yet for AWS with a patched guest OS - this would be interesting to see on instances with and without PCID support.
I had a question, the author states:
>"The PCID (Processor-Context ID) feature on x86-64 works much like the more generic ASID (Address Space IDs)"
Is ASID the RISC instruction that accomplishes the same thing that PCID does on x86 then?
Can PCID (like HyperThreading, full L3 cache, or extra PCI-e slots in the latest i7s and i9s) be enabled with an update that blows those (e)fuses.
I created script for detecting system status against Meltdown issue if anyone is interested if system is patched: https://gist.github.com/Szpadel/003798ac7f4d98bc3583c2a5f306...
One thing I still don't understand about all this:
Why is there still a (smaller) performance hit from the KPTI patch when PCID is used?
One problem is cross-vendor migration, because AMD don't support PCID.
I hate that you can't even view Google groups without an account. It also requires us to do nothing but show text. To me groups and blogger has always represented what a terrible web application is.
For practical purposes, I believe 4th Gen Intel (Haswell) was the first to implement PCID. The 2015 15" MacBook Pro uses Haswell.
Many people said that if your processor support PCID, the performance will not be reduced a lot by the new patches. However, after installing new updates for windows and for my very new CPU 7600U everything becomes extremely slow. My laptop is now literally unusable. Even the simplest tasks are very slow. Before this update I was able to watch youtube videos in 4K, now I'm struggling even to watch 480p... I will never buy Intel processors again. In the last few months I only hear lies from Intel regarding Meltdown, Management Engine and other "holes" in their products. Now I can throw my super expensive laptop in garbage. Thank you Intel.