On 10/25/2016 11:03 AM, Christian Borntraeger wrote: > Peter, > > here is v2 with some improved patch descriptions and some fixes. The > previous version has survived one day of linux-next and I only changed > small parts. > So unless there is some other issue, feel free to pull (or to apply > the patches) to tip/locking. > > The following changes since commit 07d9a380680d1c0eb51ef87ff2eab5c994949e69: > > Linux 4.9-rc2 (2016-10-23 17:10:14 -0700) > > are available in the git repository at: > > git://git.kernel.org/pub/scm/linux/kernel/git/borntraeger/linux.git tags/cpurelax > > for you to fetch changes up to dcc37f9044436438360402714b7544a8e8779b07: > > processor.h: remove cpu_relax_lowlatency (2016-10-25 09:49:57 +0200) Ping. Peter, you had these patches in your https://git.kernel.org/cgit/linux/kernel/git/peterz/queue.git/ repository, but now the patches are gone. Any feedback? > > ---------------------------------------------------------------- > cpu_relax: drop lowlatency, introduce yield > > For spinning loops people do often use barrier() or cpu_relax(). > For most architectures cpu_relax and barrier are the same, but on > some architectures cpu_relax can add some latency. > For example on power,sparc64 and arc, cpu_relax can shift the CPU > towards other hardware threads in an SMT environment. > On s390 cpu_relax does even more, it uses an hypercall to the > hypervisor to give up the timeslice. > In contrast to the SMT yielding this can result in larger latencies. > In some places this latency is unwanted, so another variant > "cpu_relax_lowlatency" was introduced. Before this is used in more > and more places, lets revert the logic and provide a cpu_relax_yield > that can be called in places where yielding is more important than > latency. By default this is the same as cpu_relax on all architectures. > > So my proposal boils down to: > - lowest latency: use barrier() or mb() if necessary > - low latency: use cpu_relax (e.g. might give up some cpu for the other > _hardware_ threads) > - really give up CPU: use cpu_relax_yield > > PS: In the long run I would also try to provide for s390 something > like cpu_relax_yield_to with a cpu number (or just add that to > cpu_relax_yield), since a yield_to is always better than a yield as > long as we know the waiter. > > ---------------------------------------------------------------- > Christian Borntraeger (5): > processor.h: introduce cpu_relax_yield > stop_machine: yield CPU during stop machine > s390: make cpu_relax a barrier again > processor.h: Remove cpu_relax_lowlatency users > processor.h: remove cpu_relax_lowlatency > > arch/alpha/include/asm/processor.h | 2 +- > arch/arc/include/asm/processor.h | 4 ++-- > arch/arm/include/asm/processor.h | 2 +- > arch/arm64/include/asm/processor.h | 2 +- > arch/avr32/include/asm/processor.h | 2 +- > arch/blackfin/include/asm/processor.h | 2 +- > arch/c6x/include/asm/processor.h | 2 +- > arch/cris/include/asm/processor.h | 2 +- > arch/frv/include/asm/processor.h | 2 +- > arch/h8300/include/asm/processor.h | 2 +- > arch/hexagon/include/asm/processor.h | 2 +- > arch/ia64/include/asm/processor.h | 2 +- > arch/m32r/include/asm/processor.h | 2 +- > arch/m68k/include/asm/processor.h | 2 +- > arch/metag/include/asm/processor.h | 2 +- > arch/microblaze/include/asm/processor.h | 2 +- > arch/mips/include/asm/processor.h | 2 +- > arch/mn10300/include/asm/processor.h | 2 +- > arch/nios2/include/asm/processor.h | 2 +- > arch/openrisc/include/asm/processor.h | 2 +- > arch/parisc/include/asm/processor.h | 2 +- > arch/powerpc/include/asm/processor.h | 2 +- > arch/s390/include/asm/processor.h | 4 ++-- > arch/s390/kernel/processor.c | 4 ++-- > arch/score/include/asm/processor.h | 2 +- > arch/sh/include/asm/processor.h | 2 +- > arch/sparc/include/asm/processor_32.h | 2 +- > arch/sparc/include/asm/processor_64.h | 2 +- > arch/tile/include/asm/processor.h | 2 +- > arch/unicore32/include/asm/processor.h | 2 +- > arch/x86/include/asm/processor.h | 2 +- > arch/x86/um/asm/processor.h | 2 +- > arch/xtensa/include/asm/processor.h | 2 +- > drivers/gpu/drm/i915/i915_gem_request.c | 2 +- > drivers/vhost/net.c | 4 ++-- > kernel/locking/mcs_spinlock.h | 4 ++-- > kernel/locking/mutex.c | 4 ++-- > kernel/locking/osq_lock.c | 6 +++--- > kernel/locking/qrwlock.c | 6 +++--- > kernel/locking/rwsem-xadd.c | 4 ++-- > kernel/stop_machine.c | 2 +- > lib/lockref.c | 2 +- > 42 files changed, 53 insertions(+), 53 deletions(-) > -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
