Re: [dpdk-dev] [PATCH v5 2/4] examples: add lthread subsystem for performance-thread

["Betts, Ian" <ian.betts@intel.com>]

On Thu, Dec 03, 2015 at 08:31:39AM -0800, Stephen Hemminger wrote:
> On Thu,  3 Dec 2015 09:28:23 +0000
> ibetts <ian.betts@intel.com> wrote:
> 
> > +/*
> > + * Atomically set a value and return the old value  */ static 
> > +inline uint64_t atomic64_xchg(uint64_t *ptr, uint64_t val) 
> > +__attribute__ ((always_inline)); static inline uint64_t 
> > +atomic64_xchg(uint64_t *ptr, uint64_t val)
> 
> You don't need a forward declaration for this.
> Instead do:
> 
> static inline uint64_t __attribute__((always_inline)) 
> atomic_xchg64(uint64_t *ptr, uint64_t val)
> 
> Really should be in rte_atomic.h as a primitive and the assembly macro 
> is missing change to ptr so Gcc might optmize it away.
> 
> Something like this mayb?
> 
> static inline uint64_t __attribute__ ((always_inline)); 
> rte_atomic64_xchg(uint64_t *ptr, uint64_t val) {
> 	asm volatile (
> 			MPLOCKED
> 			"xchgq %[ptr],%[val];"
> 			: [val] "=r" (val)
>                           [ptr] "=m" (*ptr)
> 			: [ptr] "m" (*ptr),
> 			  "a" (val)
> 			: "memory");
> 
> 	return val;
> }

>-----Original Message-----
>From: Richardson, Bruce 
>Sent: Thursday, December 3, 2015 4:46 PM
>To: Stephen Hemminger
>Cc: Betts, Ian; dev@dpdk.org
>Subject: Re: [dpdk-dev] [PATCH v5 2/4] examples: add lthread subsystem for performance-thread

>Rather than using assembly, I believe the gcc builtin __sync_lock_test_and_set is actually an xchg op, so can be used here.

Thanks for the suggestion Bruce, I had looked for a builin I must have missed it.
I just tested it and its fine.
 


/Bruce