Messages in this thread | | | Date | Thu, 13 Aug 2009 14:21:44 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] Use bool for boolean flag in printk_once() |
| |
On Thu, 13 Aug 2009 13:48:26 -0700 Roland Dreier <rdreier@cisco.com> wrote:
> Using the type bool (instead of int) for the __print_once flag in the > printk_once() macro matches the intent of the code better, and allows > the compiler to generate smaller code; eg a typical callsite with gcc > 4.3.3 on i386: > > add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-6 (-6) > function old new delta > static.__print_once 4 1 -3 > get_cpu_vendor 146 143 -3 > > Saving 6 bytes of object size per callsite by slightly improving the > readability of the source seems like a win to me. > > Signed-off-by: Roland Dreier <rolandd@cisco.com> > --- > include/linux/kernel.h | 4 ++-- > 1 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h > index d6320a3..f828ce9 100644 > --- a/include/linux/kernel.h > +++ b/include/linux/kernel.h > @@ -249,10 +249,10 @@ extern bool printk_timed_ratelimit(unsigned long *caller_jiffies, > * Print a one-time message (analogous to WARN_ONCE() et al): > */ > #define printk_once(x...) ({ \ > - static int __print_once = 1; \ > + static bool __print_once = true; \ > \ > if (__print_once) { \ > - __print_once = 0; \ > + __print_once = false; \ > printk(x); \ > } \ > })
hm, OK, in trace_recursive_lock() we get:
cmpl $0, __print_once.28104(%rip) #, __print_once je .L719 #,
changed to
cmpb $0, __print_once.28104(%rip) # __print_once je .L719 #,
so the compiler used a byte for the bool.
Interestingly that bool is in section `data'. I bet printk_once() should use __read_mostly.
Also, that bool still uses four bytes of storage:
text data bss dec hex filename 22527 1445 6392 30364 769c kernel/trace/ring_buffer.o 22524 1445 6392 30361 7699 kernel/trace/ring_buffer.o (patched)
I wonder if there's some way in which we could/should cause all these little random __read_mostly bytes to get packed together somewhere.
| |