* Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > On Fri, 25 Nov 2016, Ingo Molnar wrote: > > > > > * tip-bot for Tim Chen <tipbot@xxxxxxxxx> wrote: > > > > > Commit-ID: 5e76b2ab36b40ca33023e78725bdc69eafd63134 > > > Gitweb: http://git.kernel.org/tip/5e76b2ab36b40ca33023e78725bdc69eafd63134 > > > Author: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> > > > AuthorDate: Tue, 22 Nov 2016 12:23:55 -0800 > > > Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > > CommitDate: Thu, 24 Nov 2016 20:44:19 +0100 > > > > > > x86: Enable Intel Turbo Boost Max Technology 3.0 > > > > This patch doesn't build: > > > > Note that this patch has to be redone anyway, as it won't even build: > > The branch where I merged it to builds fine. Indeed you are right - asm/mutex.h is gone in locking/core, so this is a semantic merge conflict, not a build failure. > Though, yes I missed the asm/mutex.h include which obviously should be > linux/mutex.h > > > > +#include <linux/sched.h> > > > +#include <linux/cpumask.h> > > > +#include <linux/cpuset.h> > > > +#include <asm/mutex.h> > > > +#include <linux/sched.h> > > > +#include <linux/sysctl.h> > > > +#include <linux/nodemask.h> > > > > arch/x86/kernel/itmt.c:26:23: fatal error: asm/mutex.h: No such file or directory > > > > > +config SCHED_ITMT > > > + bool "Intel Turbo Boost Max Technology (ITMT) scheduler support" > > > + depends on SCHED_MC && CPU_SUP_INTEL && X86_INTEL_PSTATE > > > + ---help--- > > > + ITMT enabled scheduler support improves the CPU scheduler's decision > > > + to move tasks to cpu core that can be boosted to a higher frequency > > > + than others. It will have better performance at a cost of slightly > > > + increased overhead in task migrations. If unsure say N here. > > > > Argh, so the 'itmt' name really sucks as well - could we please make it something > > more obvious - like SCHED_INTEL_TURBO or so - and similarly rename the file as > > well? > > > > The sched_intel_turbo.c file could thus host all things related to scheduler > > support of turbo frequencies - it shouldn't be named after the Intel acronym of > > the day... > > It would be nice to come up with such nitpicks during review. This thing went > through 8 iterations, but nothing came up and I didn't mind the itmt naming. Yeah, so I had to NAK an early iteration and didn't get around to doing a really detailed review yet - and after (falsely) thinking it had a build failure I got overly worked up about the bad naming: my bad and apologies! So the code looks good to me but the naming still sucks a bit - I'm fine with having the commits re-merged as-is and renaming the Kconfig variable to something more expressive: I've done this in tip:sched/core and have fixed the asm/mutex.h thing as well. Wrt. improving the naming: Firstly, popular tech news has coined the 'Turbo Boost Max' technology 'TBM' (TBM2 and TBM3) as the natural acronym of the Intel feature - not 'ITMT'. So to anyone except people well aware of Intel acronyms the term 'ITMT' will be pretty meaningless. Does something more generic like SCHED_MC_PRIO (as an extension to SCHED_MC) work with everyone? Intel Turbo Max 3.0 is the current (only) implementation of it, but I don't think the technology will stop at that stage as dies are getting larger but thinner. I also think the Kconfig text is somewhat misleading and the default-disabled status is counterproductive: +config SCHED_ITMT + bool "Intel Turbo Boost Max Technology (ITMT) scheduler support" + depends on SCHED_MC && CPU_SUP_INTEL && X86_INTEL_PSTATE + ---help--- + ITMT enabled scheduler support improves the CPU scheduler's decision + to move tasks to cpu core that can be boosted to a higher frequency + than others. It will have better performance at a cost of slightly + increased overhead in task migrations. If unsure say N here. ... the extra cost of smarter CPU selection is IMHO overwhelmed by the negative effects of not knowing about core frequency ordering, on most workloads. A better default would be default-y I believe (that is what we do for CPU hardware enablement typically), and a better description would be something like: +config SCHED_MC_PRIO + bool "CPU core priorities scheduler support" + depends on SCHED_MC && CPU_SUP_INTEL && X86_INTEL_PSTATE + default y + ---help--- + Intel Turbo Boost Max 3.0 enabled CPUs have a core ordering determined at + manufacturing time, which allows certain cores to reach higher turbo + frequencies (when running single threaded workloads) than others. + + Enabling this kernel feature teaches the scheduler about the TBM3 priority + order of the CPU cores and adjusts the scheduler's CPU selection logic + accordingly, so that higher overall system performance can be achieved. + + This feature will have no effect on CPUs without this feature. + + If unsure say Y here. If/when other architectures make use of this the Kconfig entry can be moved into the scheduler Kconfig - but for the time being it can stay in arch/x86/. Another variant would be to eliminate the Kconfig option altogether and make it a natural feature of SCHED_MC (like it is in the core scheduler). Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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