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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Jun 17, 2020 at 11:08:32AM +0100, Will Deacon wrote: > On Wed, Jun 17, 2020 at 10:40:54AM +0100, Dave Martin wrote: > > On Tue, Jun 16, 2020 at 06:19:27PM +0100, Will Deacon wrote: > > > diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c > > > index d9eee9194511..55c8f3ec6705 100644 > > > --- a/arch/arm64/kernel/fpsimd.c > > > +++ b/arch/arm64/kernel/fpsimd.c > > > @@ -349,7 +349,7 @@ static unsigned int find_supported_vector_length(unsigned int vl) > > > return sve_vl_from_vq(__bit_to_vq(bit)); > > > } > > > > > > -#ifdef CONFIG_SYSCTL > > > +#if defined(CONFIG_ARM64_SVE) && defined(CONFIG_SYSCTL) > > > > > > static int sve_proc_do_default_vl(struct ctl_table *table, int write, > > > void *buffer, size_t *lenp, loff_t *ppos) > > > @@ -394,9 +394,9 @@ static int __init sve_sysctl_init(void) > > > return 0; > > > } > > > > > > -#else /* ! CONFIG_SYSCTL */ > > > +#else /* ! (CONFIG_ARM64_SVE && CONFIG_SYSCTL) */ > > > static int __init sve_sysctl_init(void) { return 0; } > > > -#endif /* ! CONFIG_SYSCTL */ > > > +#endif /* ! (CONFIG_ARM64_SVE && CONFIG_SYSCTL) */ > > > > Hmm, I guess that works, but it still seems cumbersome. #ifdefs do > > tend to breed as the code gets extended, so I'd worked hard to > > eliminate them as much as possible. > > This is just extending an existing #ifdef though, and I don't think it > makes any sense to compile in the SVE sysctl logic if SVE is not enabled. > If CONFIG_SYSCTL didn't exist, this code would almost certainly be inside > a CONFIG_SVE block anyway. Only code that's unreachable from inside the translation unit needs to be #ifdeffed. For the rest, the compiler knows how to determine what's used (indeed, it's better at it than humans). Originally I relied on #ifdefs more, but I needed a lot of them, and it was hell to rebase every time anything needed to be moved around. Currently I don't see anything that gets compiled in if CONFIG_SYSCTL=n. Other than what was already compiled before this patch. We still need to track the default vl, because it depends on the hardware; however it's effectively ro-after-init if CONFIG_SYSCTL=n. I think that complicating the #ifdef conditions in this file is a slippery slope, but I guess it's the it's up to the maintainer whether to care about that. Am I missing something? > > Can't we simply leave the helpers outside the #ifdef, and do this? > > > > /* Default VL for tasks that don't set it explicitly: */ > > static int __sve_default_vl = -1; > > > > -static int get_sve_default_vl(void) > > +static inline int get_sve_default_vl(void) > > { > > return READ_ONCE(__sve_default_vl); > > } > > > > -static void set_sve_default_vl(int val) > > +static inline void set_sve_default_vl(int val) > > { > > WRITE_ONCE(__sve_default_vl, val); > > } > > That would work too, although I'd be wary of somebody removing the inline > later on because "the compiler knows best about inlining decisions". I'd AFAIK inline is widely used for static functions in headers for precisely this reason. I have tried to use __maybe_unused (or even #ifdefs) in the past to be more explicit, but got shouted at. We could optionally use __maybe_unused here if you think that's more self-explanatory. > also say that calling set_sve_default_vl() is an error if CONFIG_SVE is > not defined as we really want get_sve_default_vl() to return -1 > unconditionally in that case. Having set_sve_default_vl() inside the > #ifdef ensures that. Fair point, I'm not sure how valuable it is. We manage without it thus far: prior to these changes, the sve_default_vl variable was not #ifdeffed. > I don't care too strongly either way, but I already queued my diff last > night [1] in order to fix linux-next, so I'd prefer not to drop it unless > there's a functional reason to do so. Ack, since this change would be purely to ease future maintanence (or not, if you judge it's not useful), it's not urgent. Cheers ---Dave _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel