[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 17/32] arm: define __smp_xxx
On Mon, Jan 04, 2016 at 01:59:34PM +0000, Russell King - ARM Linux wrote: > On Mon, Jan 04, 2016 at 02:54:20PM +0100, Peter Zijlstra wrote: > > On Mon, Jan 04, 2016 at 02:36:58PM +0100, Peter Zijlstra wrote: > > > On Sun, Jan 03, 2016 at 11:12:44AM +0200, Michael S. Tsirkin wrote: > > > > On Sat, Jan 02, 2016 at 11:24:38AM +0000, Russell King - ARM Linux > > > > wrote: > > > > > > > > My only concern is that it gives people an additional handle onto a > > > > > "new" set of barriers - just because they're prefixed with __* > > > > > unfortunately doesn't stop anyone from using it (been there with > > > > > other arch stuff before.) > > > > > > > > > > I wonder whether we should consider making the smp memory barriers > > > > > inline functions, so these __smp_xxx() variants can be undef'd > > > > > afterwards, thereby preventing drivers getting their hands on these > > > > > new macros? > > > > > > > > That'd be tricky to do cleanly since asm-generic depends on > > > > ifndef to add generic variants where needed. > > > > > > > > But it would be possible to add a checkpatch test for this. > > > > > > Wasn't the whole purpose of these things for 'drivers' (namely > > > virtio/xen hypervisor interaction) to use these? > > > > Ah, I see, you add virt_*mb() stuff later on for that use case. > > > > So, assuming everybody does include asm-generic/barrier.h, you could > > simply #undef the __smp version at the end of that, once we've generated > > all the regular primitives from it, no? > > Not so simple - that's why I mentioned using inline functions. > > The new smp_* _macros_ are: > > +#define smp_mb() __smp_mb() > > which means if we simply #undef __smp_mb(), smp_mb() then points at > something which is no longer available, and we'll end up with errors > saying that __smp_mb() doesn't exist. > > My suggestion was to change: > > #ifndef smp_mb > #define smp_mb() __smp_mb() > #endif > > to: > > #ifndef smp_mb > static inline void smp_mb(void) > { > __smp_mb(); > } > #endif > > which then means __smp_mb() and friends can be #undef'd afterwards. Absolutely, I got it. The issue is that e.g. tile has: #define __smp_mb__after_atomic() do { } while (0) and this is cheaper than barrier(). For this reason I left #define smp_mb__after_atomic() __smp_mb__after_atomic() in place there. Now, of course I can do (in asm-generic): #ifndef smp_mb__after_atomic static inline void smp_mb__after_atomic(void) { ... } #endif but this seems ugly: architectures do defines, generic version does inline. And that is not all: APIs like smp_store_mb can take a variety of types as arguments so they pretty much must be implemented as macros. Teaching checkpatch.pl to complain about it seems like the cleanest approach. > -- > RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/ > FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up > according to speedtest.net. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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