On Mon, 2016-11-28 at 09:51 +0100, Ingo Molnar wrote: > * Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > > > > > > > > > > > > > > > +#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). > I am fine with renaming SCHED_ITMT to SCHED_MC_PRIO. Patch 7 and 8 that Rafael merged into his tree also have SCHED_ITMT so they will need to be updated if we renamed it. Thanks. Tim -- 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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