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SubjectRe: [PATCH 0/3] nohz: Convert tick dependency mask to atomic_t
On Fri, Mar 25, 2016 at 09:48:47AM +0100, Ingo Molnar wrote:
>
> * Frederic Weisbecker <fweisbec@gmail.com> wrote:
>
> > As per Linus suggestion, lets convert the tick dependency mask to
> > atomic_t. Introduce atomic_fetch_or() and confine fetch_or() back to
> > scheduler guts.
> >
> > git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> > timers/nohz
> >
> > HEAD: 7b7e5da5733f58668181077ec394a718e08c392c
> >
> > Thanks,
> > Frederic
> > ---
> >
> > Frederic Weisbecker (3):
> > atomic: Introduce atomic_fetch_or
> > nohz: Convert tick dependency mask to atomic_t
> > Revert "atomic: Export fetch_or()"
> >
> >
> > include/linux/atomic.h | 34 +++++++++++++--------------
> > include/linux/sched.h | 4 ++--
> > kernel/sched/core.c | 18 ++++++++++++++
> > kernel/time/tick-sched.c | 61 ++++++++++++++++++++++++------------------------
> > kernel/time/tick-sched.h | 2 +-
> > 5 files changed, 68 insertions(+), 51 deletions(-)
>
> Could you please also convert the sched/core.c usage, so that we can get rid of
> the private fetch_or() definition? Please also double check that it does not
> result in worse code generation.

That involve converting thread_info::flags to atomic_t and given how much the type varies
across architectures:

$ grep 'flags;' $(ls arch/*/include/asm/thread_info.h)
arch/alpha/include/asm/thread_info.h: unsigned int flags; /* low level flags */
arch/arc/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/arm64/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/arm/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/avr32/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/blackfin/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/c6x/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/cris/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/frv/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/h8300/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/hexagon/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/ia64/include/asm/thread_info.h: __u32 flags; /* thread_info flags (see TIF_*) */
arch/m32r/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/m68k/include/asm/thread_info.h: unsigned long flags;
arch/metag/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/microblaze/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/mips/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/mn10300/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/nios2/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/openrisc/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/parisc/include/asm/thread_info.h: unsigned long flags; /* thread_info flags (see TIF_*) */
arch/powerpc/include/asm/thread_info.h: unsigned long local_flags; /* private flags for thread */
arch/s390/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/score/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/sh/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/tile/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/um/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/unicore32/include/asm/thread_info.h: unsigned long flags; /* low level flags */
arch/x86/include/asm/thread_info.h: __u32 flags; /* low level flags */
arch/xtensa/include/asm/thread_info.h: unsigned long flags; /* low level flags */

also given how much it is accessed (and that happens a lot in ASM as well). This conversion deserves quite a
whole project on its own.

It might be possible to do it incrementally though.

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