Messages in this thread | | | Date | Thu, 31 Mar 2016 08:54:19 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 0/3] nohz: Convert tick dependency mask to atomic_t |
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* Frederic Weisbecker <fweisbec@gmail.com> wrote:
> On Tue, Mar 29, 2016 at 03:05:14PM +0200, Ingo Molnar wrote: > > > > * Ingo Molnar <mingo@kernel.org> wrote: > > > > > > > > * Linus Torvalds <torvalds@linux-foundation.org> wrote: > > > > > > > On Tue, Mar 29, 2016 at 4:44 AM, Ingo Molnar <mingo@kernel.org> wrote: > > > > > > > > > > Harmonizing thread_info::flags does not look easy, given how much assembly code > > > > > accesses this field. > > > > > > > > It might not be too bad. > > > > > > > > For 32-bit architectures (which is still most of them), it's just a > > > > > > > > unsigned int/long -> atomic_t > > > > > > > > and for 64-bit architectures you end up with three choices: > > > > > > > > - it's already 32-bit (alpha, ia64, x86): > > > > > > > > unsigned int -> atomic_t > > > > > > > > - little-endian long: > > > > > > > > atomic_t flags > > > > unsigned int padding; > > > > > > > > - big-endian long (only powerpc? Maybe there's a big-endian MIPS still?) > > > > > > > > unsigned int padding; > > > > atomic_t flags; > > > > > > Hm, that indeed sounds fairly nice and doable - I thought some architectures do > > > have a task flag above bit 31, but that does not appear to be so ... > > > > > > Right now we seem to have 27 bits defined in include/linux/sched.h, with 5 more > > > bits left for the future. Here's their current usage histogram in the kernel > > > source: > > > > > > PF_KTHREAD : 68 > > > PF_MEMALLOC : 65 > > > > Argh, my reading comprehension skills suck today. > > > > That's a totally useless analysis of task_struct::flags, while we want to convert > > thread_info::flags... > > Actually we want to convert that one too :-) > In fact I planned to start there.
Sounds good to me! I also volunteer the x86 architecture to be the guinea pig to convert thread_info::flags to atomic_t ;-) [*]
Thanks,
Ingo
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