[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] Don't trigger unnecessary shadow scans on p2m entry update
On 25/11/2011 08:45, "Jan Beulich" <JBeulich@xxxxxxxx> wrote: >>>> On 24.11.11 at 19:31, Keir Fraser <keir.xen@xxxxxxxxx> wrote: >> On 24/11/2011 17:58, "Andres Lagar-Cavilla" <andres@xxxxxxxxxxxxxxxx> wrote: >>> @@ -815,6 +815,12 @@ static inline unsigned long vtlb_lookup( >>> } >>> #endif /* (SHADOW_OPTIMIZATIONS & SHOPT_VIRTUAL_TLB) */ >>> >>> +static inline int __check_page_no_refs(struct page_info *page) >>> +{ >>> + unsigned long __count = page->count_info; >>> + return ( (__count & PGC_count_mask) == >>> + ((__count & PGC_allocated) ? 1 : 0) ); >> >> It's a fussy point, but it might be better to use >> atomic_read_ulong(&page->count_info) here, to ensure that the compiler reads >> the field once only. It's cheap (compiles to a single mov instruction), but >> atomic_read_ulong doesn't exist so you'd have to add its (obvious) >> definition to asm-x86/atomic.h > > I think Tim suggested anyway to use > > (__count & (PGC_count_mask|PGC_allocated)) matched against > (1|PGC_allocated) here, which would eliminate the multiple read > potential if used in a switch statement. Yes, that would be better. -- Keir > Also, for clarity the function should probably return bool_t. > > Jan > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
|
Lists.xenproject.org is hosted with RackSpace, monitoring our |