Messages in this thread | | | Date | Tue, 15 Mar 2016 13:15:25 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] nohz: Change tick_dep_mask from 'unsigned long' to 'unsigned int' |
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* Ingo Molnar <mingo@kernel.org> wrote:
> > Linus noticed that the new tick_dep_mask types introduced in: > > d027d45d8a17 ("nohz: New tick dependency mask") > > ... are sloppily defined as 'unsigned long' - which is wasteful > to carry just 4 bits and which may also create suboptimal data > types on 64-bit systems with word alignment padding holes in them. > > Fix this by changing the type to the more natural 'unsigned int'. > > (The xchg_or() API will work fine with 'unsigned int' as well.) > > Reported-by: Linus Torvalds <torvalds@linux-foundation.org> > Cc: Chris Metcalf <cmetcalf@ezchip.com> > Cc: Frederic Weisbecker <fweisbec@gmail.com> > Cc: Christoph Lameter <cl@linux.com> > Cc: Chris Metcalf <cmetcalf@ezchip.com> > Cc: Ingo Molnar <mingo@kernel.org> > Cc: Luiz Capitulino <lcapitulino@redhat.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Rik van Riel <riel@redhat.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Viresh Kumar <viresh.kumar@linaro.org> > Signed-off-by: Ingo Molnar <mingo@kernel.org> > --- > include/linux/sched.h | 4 ++-- > kernel/time/tick-sched.c | 11 +++++------ > 2 files changed, 7 insertions(+), 8 deletions(-)
Hm, so the problem I did not consider is the following:
triton:~/tip> git grep tick_dep_mask kernel | grep _bit kernel/time/tick-sched.c: clear_bit(bit, &tick_dep_mask); kernel/time/tick-sched.c: clear_bit(bit, &ts->tick_dep_mask); kernel/time/tick-sched.c: clear_bit(bit, &tsk->tick_dep_mask); kernel/time/tick-sched.c: clear_bit(bit, &sig->tick_dep_mask);
and the bitops natural type (and in fact the only supported bitops type) is 'unsigned long'.
So it's not that easy to change a bitmask over to unsigned int.
Suggestions?
Thanks,
Ingo
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