Messages in this thread | | | Subject | Re: [PATCH] sched/cputime: silence a -Wunused-function warning | From | Joe Perches <> | Date | Fri, 06 Mar 2020 10:38:06 -0800 |
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On Fri, 2020-03-06 at 09:25 -0800, Joe Perches wrote: > On Fri, 2020-03-06 at 09:13 -0800, Nick Desaulniers wrote: > > On Fri, Mar 6, 2020 at 7:42 AM Qian Cai <cai@lca.pw> wrote: > > > account_other_time() is only used when CONFIG_IRQ_TIME_ACCOUNTING=y (in > > > irqtime_account_process_tick()) or CONFIG_VIRT_CPU_ACCOUNTING_GEN=y (in > > > get_vtime_delta()). When both are off, it will generate a compilation > > > warning from Clang, > > > > > > kernel/sched/cputime.c:255:19: warning: unused function > > > 'account_other_time' [-Wunused-function] > > > static inline u64 account_other_time(u64 max) > > > > > > Rather than wrapping around this function with a macro expression, > > > > > > if defined(CONFIG_IRQ_TIME_ACCOUNTING) || \ > > > defined(CONFIG_VIRT_CPU_ACCOUNTING_GEN) > > > > > > just use __maybe_unused for this small function which seems like a good > > > trade-off. > > > > Generally, I'm not a fan of __maybe_unused. It is a tool in the > > toolbox for solving this issue, but it's my least favorite. Should > > the call sites be eliminated, this may mask an unused and entirely > > dead function from being removed. Preprocessor guards based on config > > give more context into *why* a particular function may be unused. > > > > So let's take a look at the call sites of account_other_time(). Looks > > like irqtime_account_process_tick() (guarded by > > CONFIG_IRQ_TIME_ACCOUNTING) and get_vtime_delta() (guarded by > > CONFIG_VIRT_CPU_ACCOUNTING_GEN). If it were one config guard, then I > > would prefer to move the definition to be within the same guard, just > > before the function definition that calls it, but we have a more > > complicated case here. > > > > The next thing I'd check to see is if there's a dependency between > > configs. In this case, both CONFIG_IRQ_TIME_ACCOUNTING and > > CONFIG_VIRT_CPU_ACCOUNTING_GEN are defined in init/Kconfig. In this > > case there's also no dependency between configs, so specifying one > > doesn't imply the other; so guarding on one of the two configs is also > > not an option. > > > > So, as much as I'm not a fan of __maybe_unused, it is indeed the > > simplest option. Though, I'd still prefer the ifdef you describe > > instead, maybe the maintainers can provide guidance/preference? > > Another option might be to move static inline functions > where possible to an #include file (like sched.h) but the > same possible dead function issue would still exist.
Turns out there are hundreds of unused static inline functions in kernel .h files.
A trivial script to find some of them (with likely false positives as some might actually be used via ## token pasting mechanisms).
(and there's almost certainly a better way to do this too as it takes a _very_ long time to run)
$ grep-2.5.4 -rP --include=*.h '^[ \t]*static\s+inline\s+(?:\w+\s+){1,3}\w+[ \t]*\(' * | \ grep -P -oh '\w+\s*\(' | \ sort | uniq -c | sort -n | grep -P '^\s+1\b' | \ sed -r -e 's/^\s+1\s+//' -e 's/\(//' | \ while read line ; do \ echo -n "$line: " ; git grep -w $line | wc -l ; \ done | \ grep ": 1$"
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