On Mon, May 11, 2015 at 07:57:22PM +0200, Denys Vlasenko wrote: > With both gcc 4.7.2 and 4.9.2, sometimes gcc mysteriously doesn't inline > very small functions we expect to be inlined. In particular, > with this config: http://busybox.net/~vda/kernel_config > there are more than a thousand copies of tiny spinlock-related functions: > > $ nm --size-sort vmlinux | grep -iF ' t ' | uniq -c | grep -v '^ *1 ' | sort > -rn | grep ' spin' > 473 000000000000000b t spin_unlock_irqrestore > 292 000000000000000b t spin_unlock > 215 000000000000000b t spin_lock > 134 000000000000000b t spin_unlock_irq > 130 000000000000000b t spin_unlock_bh > 120 000000000000000b t spin_lock_irq > 106 000000000000000b t spin_lock_bh > > Disassembly: > > ffffffff81004720 <spin_lock>: > ffffffff81004720: 55 push %rbp > ffffffff81004721: 48 89 e5 mov %rsp,%rbp > ffffffff81004724: e8 f8 4e e2 02 callq <_raw_spin_lock> > ffffffff81004729: 5d pop %rbp > ffffffff8100472a: c3 retq
Frame pointers make this even more awful, since without them this could just become a single jmp. (Assuming _raw_spin_lock shouldn't be inlined too.) > This patch fixes this via s/inline/__always_inline/ in spinlock.h. > This decreases vmlinux by about 30k: > > text data bss dec hex filename > 82375570 22255544 20627456 125258570 7774b4a vmlinux.before > 82335059 22255416 20627456 125217931 776ac8b vmlinux Nice improvement. Given that this actually makes the kernel *smaller*, presumably in addition to faster, this forced inlining seems completely reasonable. > Signed-off-by: Denys Vlasenko <dvlas...@redhat.com> > Cc: Thomas Graf <tg...@suug.ch> > Cc: David S. Miller <da...@davemloft.net> > Cc: Bart Van Assche <bvanass...@acm.org> > Cc: Peter Zijlstra <pet...@infradead.org> > Cc: David Rientjes <rient...@google.com> > Cc: David S. Miller <da...@davemloft.net> > Cc: Andrew Morton <a...@linux-foundation.org> > Cc: Linus Torvalds <torva...@linux-foundation.org> > Cc: Oleg Nesterov <o...@redhat.com> > Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com> > Cc: Ingo Molnar <mi...@kernel.org> > Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com> > CC: linux-kernel@vger.kernel.org Reviewed-by: Josh Triplett <j...@joshtriplett.org> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
