what does the code mean?

shitou · 11-30-2010, 04:08 AM

/* Conditionally execute fence after interlocked instruction. */
static INLINE void
AtomicEpilogue(void)
{
#ifdef ATOMIC_USE_FENCE
#ifdef VMM
/* The monitor conditionally patches out the lfence when not needed.*/
/* Construct a MonitorPatchTextEntry in the .patchtext section. */
asm volatile ("1:\n\t"
"lfence\n\t"
"2:\n\t"
".pushsection .patchtext\n\t"
".quad 1b\n\t"
".quad 2b\n\t"
".popsection\n\t" ::: "memory");
#else
if (UNLIKELY(AtomicUseFence)) {
asm volatile ("lfence" ::: "memory");
}
#endif
#endif

frankbell · 12-01-2010, 08:39 PM

It might help if you told folks where that code came from.

If it's kernel code, you might try looking for manuals and tutorials about the kernel.

I searched for

Quote:

The monitor conditionally patches out the lfence when not needed

and came up with

http://lkml.indiana.edu/hypermail/li....0/author.html

Kenny_Strawn · 12-02-2010, 05:16 AM

Googling "static INLINE void AtomicEpilogue (void)" took me to this:

http://www.google.com/url?sa=t&sourc...qJZR-g&cad=rja

Apparently, the file that includes this code mentioned in the original post is called "vm_atomic.h" and the function is called "AtomicEpilogue()":

Code:

static INLINE void
AtomicEpilogue(void)
{
#ifdef ATOMIC_USE_FENCE
#ifdef VMM
      /* The monitor conditionally patches out the lfence when not needed.*/
      /* Construct a MonitorPatchTextEntry in the .patchtext section. */
   asm volatile ("1:\n\t"
                 "lfence\n\t"
                 "2:\n\t"
                 ".pushsection .patchtext\n\t"
#ifdef VMM32
                 ".long 1b\n\t"
                 ".long 0\n\t"
                 ".long 2b\n\t"
                 ".long 0\n\t"
#else 
                 ".quad 1b\n\t"
                 ".quad 2b\n\t"
#endif
                 ".popsection\n\t" ::: "memory");
#else
   if (UNLIKELY(AtomicUseFence)) {
      asm volatile ("lfence" ::: "memory");
   }
#endif
#endif
}

And apparently it is made up of mostly assembly language embedded within C. Very messy, I agree.