* Frederic Weisbecker <[email protected]> wrote:
> On Fri, Mar 25, 2016 at 09:48:47AM +0100, Ingo Molnar wrote:
> >
> > * Frederic Weisbecker <[email protected]> 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:
Ah, yes - I did a similar analysis originally and then promptly forgot about it!
Harmonizing thread_info::flags does not look easy, given how much assembly code
accesses this field.
So I suspect your original series of introducing the atomic_t interface while
reverting back to the scheduler-specific auto-typing hack is fine after all.
> 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.
So I don't even know where to begin with that:
- some 64-bit architectures want 32-bit flags
- some 64-bit architectures want 64-bit flags
- some 64-bit architectures may genuinely want more than 32 flags
- some 64-bit architectures may want 64-bit word just because it's the fastest
... there's not a single natural data type on the C side that I can see this
could
be converted to :-/
Thanks,
Ingo
