Date: Thu, 20 Aug 2015 13:44:57 +0100 From: Will Green <will@sundivenetworks.com> To: freebsd-current@freebsd.org Subject: CPU Perf & Power Mgt Message-ID: <7B1D7A3F-DA20-4195-8228-7D3F07790B5C@sundivenetworks.com>
next in thread | raw e-mail | index | archive | help
Hello, I=E2=80=99ve been thinking about CPU performance and power management on = FreeBSD recently. As a user it seems like there has been little activity = in this area and I wanted to try and understand what the situation was. =46rom the publicly available information on powerd [1], the wiki [2] = and my attempts to optimize hardware power/performance; it seems the = current approach is quite old and laptop-focused. Recent CPU designs can = control the state and frequency of individual cores very quickly. In the = case of a single heavy thread, a multicore CPU might power-gate all but = one core so the active core can be pushed to a higher frequency. This = doesn=E2=80=99t seem to be possible on FreeBSD at the moment: powerd is = userland (~250 ms poll) and can only control the frequency of all cores = together. I understand this opens a can of worms as the CPU core states, frequency = and scheduler would all need to co-operate. However, I think it=E2=80=99s = important that this does happen. Without this functionality FreeBSD is = leaving performance on the table and consuming more power than other = operating systems. At BSDCan I heard that there was work going on for = arm systems, but didn=E2=80=99t manage to get any details and whether it = was relevant to amd64 too.=20 TIA, Will PS. I was interested to see Intel announce at IDF that they'll be = working with open source projects to implement "Speed Shift = Technology=E2=80=9D, which leaves responsibility for p-state management = on the CPU. [1] https://www.freebsd.org/cgi/man.cgi?query=3Dpowerd [2] https://wiki.freebsd.org/TuningPowerConsumption
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?7B1D7A3F-DA20-4195-8228-7D3F07790B5C>