unwind: enable dwarf cache of libunwind

Here is the benchmark of the dwarf cache.

Target program:

    #include <sched.h>
    int main(void)
    {
      unsigned int max = 0x6fff, i;
      for (i = 0; i < max; i++)
	sched_yield();
      return 0;
    }

Command line:

	./strace -o /dev/null -k a.out

With the dwarf cache:

    real	0m12.081s
    user	0m3.858s
    sys 	0m8.194s

Without the dwarf cache:

    real	0m22.326s
    user	0m5.218s
    sys		0m16.952s

Signed-off-by: Masatake YAMATO <yamato@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/unwind.c b/unwind.c
index 53191be4..797a287a 100644
--- a/unwind.c
+++ b/unwind.c
@@ -88,6 +88,7 @@ unwind_init(void)
 	libunwind_as = unw_create_addr_space(&_UPT_accessors, 0);
 	if (!libunwind_as)
 		error_msg_and_die("failed to create address space for stack tracing");
+	unw_set_caching_policy(libunwind_as, UNW_CACHE_GLOBAL);
 }
 
 void
@@ -139,6 +140,8 @@ build_mmap_cache(struct tcb* tcp)
 	size_t blen;
 	size_t dlen;
 
+	unw_flush_cache (libunwind_as, 0, 0);
+
 	sprintf(filename, "/proc/%d/maps", tcp->pid);
 	fp = fopen(filename, "r");
 	if (!fp) {