* Ingo Molnar <mi...@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 <torva...@linux-foundation.org>
> Cc: Chris Metcalf <cmetc...@ezchip.com>
> Cc: Frederic Weisbecker <fweis...@gmail.com>
> Cc: Christoph Lameter <c...@linux.com>
> Cc: Chris Metcalf <cmetc...@ezchip.com>
> Cc: Ingo Molnar <mi...@kernel.org>
> Cc: Luiz Capitulino <lcapitul...@redhat.com>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Rik van Riel <r...@redhat.com>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Cc: Viresh Kumar <viresh.ku...@linaro.org>
> Signed-off-by: Ingo Molnar <mi...@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
