Intel Core i7 5775C: Once Going, This Broadwell CPU Is Great On Linux
For those that didn't follow my posts earlier in the month about the i7-5775C on Linux, initially there were some headaches. As outlined here, on Ubuntu with one of the Z97 motherboards tested there were kernel panics attributed to the Intel/CPU idle driver when testing various kernels. This was, of course, on a system with a freshly updated BIOS for supporting Broadwell and swaping out various components was to no avail. The i7-5775C on Ubuntu would run into these panics frequently when under load and even with Linux 4.2 the problems persisted. I ended up finding somewhat of a workaround by enabling the "CPU OC Fixed Mode" from the UEFI/BIOS. That option, which causes the i7-5775C to run at its maximum turbo state without ever down-clocking, did alleviate the kernel panics for the most part. However, that's far from being energy efficient, etc.
When trying another Z97 motherboard, it hadn't even booted up with the i7-5775C even though the new BIOS had claimed Broadwell support. With a third Z97 motherboard tested, the MSI Z97-G45 GAMING there were still Linux problems. However, last week I finally made an interesting discovery: Fedora 22 runs great with the i7-5775C. On Fedora 22 when testing different kernels, the i7-5775C has been running 100% stable for the past week of constant Linux benchmarking. Even though multiple different kernels were tried on Ubuntu, and both OSes are using Intel Idle, Intel P-State scaling driver, etc, something about Fedora is making Broadwell happier than Ubuntu 15.04.
While I've contacted different people at Intel about these issues, to date I haven't heard back with any solution. Thus for the past week I've been happily running Core i7 5775C benchmarks under Fedora 22 without any problems. If I hear back about the issues encountered under Ubuntu, I'll be sure to post an update on Phoronix. I've been very happy with the i7-5775C under Fedora both with the processor and Iris Pro performance. These initial i7-5775C issues on Ubuntu were the biggest Intel problem I've experienced since Sandy Bridge when back then the open-source Linux graphics support wasn't in good shape at launch time, but at least this Broadwell snafu can be worked around.