Messages in this thread | | | Date | Wed, 5 Jul 2006 12:26:33 +0200 | From | Ingo Molnar <> | Subject | Re: [patch] uninline init_waitqueue_*() functions |
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* Andrew Morton <akpm@osdl.org> wrote:
> > > shrinks fs/select.o by eight bytes. (More than I expected). So > > > it does appear to be a space win, but a pretty slim one. > > > > there are 855 calls to these functions in the allyesconfig vmlinux i > > did, and i measured a combined size reduction of 34791 bytes. That > > averages to a 40 bytes win per call site. (on i386.) > > > > Yes, but that lumps all three together. init_waitqueue_head() is > obviously the porky one. And it's porkier with CONFIG_DEBUG_SPINLOCK > and CONFIG_LOCKDEP, which isn't the case to optimise for.
true. I redid my tests with both lockdep and debug-spinlocks turned off:
text data bss dec filename 21172153 6077270 3081864 30331287 vmlinux.x32.after 21198222 6077106 3081864 30357192 vmlinux.x32.before
with 851 callsites that's a 30.6 bytes win per call site (total 26K) - still not bad at all.
it's a win even on 64-bit:
text data bss dec filename 21237025 6997266 3327600 31561891 vmlinux.x64.after 21252773 6997090 3327600 31577463 vmlinux.x64.before
with 755 callsites that's still a 20.8 bytes win per call site (total 15K).
> With the debug options turned off, even init_waitqueue_head() becomes > just three assignments, similar to init_waitqueue_entry() and > init_waitqueue_func_entry(). All pretty marginal.
but three assignments could mean 3 offsets embedded in the instructions. (for init_waitqueue_entry we also embedd the address of default_wake_function) Even 3 assignments can add up to a footprint that is far from marginal.
The rough rule of thumb for inlining is that anything that is larger than one C statement is probably too large for inlining. (but even 1-line statements might be too fat at times)
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