From 0e14e0793ffb891bccd465cf518480685e3cd49e Mon Sep 17 00:00:00 2001
From: Josh Stone <jistone@redhat.com>
Date: Mon, 8 Jun 2009 15:36:42 -0700
Subject: Let query_module abort early for simple matches

query_module was already returning DW_CB_ABORT when a simple match was
found, but dwflpp::iterate_over_modules was ignoring that and instead
forcing the module loop to restart.  The only way out of the loop was
with the pending_interrupts flag, which is only for signalled
interrupts.

Now iterate_over_modules will only attempt the dwfl_getmodules loop
once, since that loop will only abort if the CB returns DW_CB_ABORT.
Then query_module is also modified to return ABORT if pending_interrupts
is flagged.

My trusty test, stap -l syscall.*, is nearly 2x faster with this change.
Empirically, I found that the kernel object is always the first "module"
returned, so the syscall probepoints always gets to short-circuit the
loop right away.
---
 dwflpp.cxx | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

(limited to 'dwflpp.cxx')

diff --git a/dwflpp.cxx b/dwflpp.cxx
index 3af26053..1a589771 100644
--- a/dwflpp.cxx
+++ b/dwflpp.cxx
@@ -397,13 +397,8 @@ dwflpp::iterate_over_modules(int (* callback)(Dwfl_Module *, void **,
                                               void *),
                              base_query *data)
 {
-  ptrdiff_t off = 0;
-  do
-    {
-      if (pending_interrupts) return;
-      off = dwfl_getmodules (dwfl, callback, data, off);
-    }
-  while (off > 0);
+  dwfl_getmodules (dwfl, callback, data, 0);
+
   // Don't complain if we exited dwfl_getmodules early.
   // This could be a $target variable error that will be
   // reported soon anyway.
-- 
cgit 


From f517ee24c58413f7de89ede71c728579c12ace5b Mon Sep 17 00:00:00 2001
From: Josh Stone <jistone@redhat.com>
Date: Mon, 8 Jun 2009 16:37:00 -0700
Subject: Remove dwflpp::default_name

It was just a basic NULL check, but creating its string temporaries was
causing a fair slowdown.  Removing this function and adjusting the
callers shaves ~5% off the syscall.* elaboration time.
---
 dwflpp.cxx | 19 ++++---------------
 1 file changed, 4 insertions(+), 15 deletions(-)

(limited to 'dwflpp.cxx')

diff --git a/dwflpp.cxx b/dwflpp.cxx
index 1a589771..74294384 100644
--- a/dwflpp.cxx
+++ b/dwflpp.cxx
@@ -84,15 +84,6 @@ dwflpp::~dwflpp()
 }
 
 
-string const
-dwflpp::default_name(char const * in, char const *)
-{
-  if (in)
-    return in;
-  return string("");
-}
-
-
 void
 dwflpp::get_module_dwarf(bool required, bool report)
 {
@@ -129,10 +120,8 @@ dwflpp::focus_on_module(Dwfl_Module * m, module_info * mi)
   mod_info = mi;
   if (m)
     {
-      module_name = default_name(dwfl_module_info(module, NULL,
-                                                  &module_start, &module_end,
-                                                  NULL, NULL, NULL, NULL),
-                                 "module");
+      module_name = dwfl_module_info(module, NULL, &module_start, &module_end,
+                                     NULL, NULL, NULL, NULL) ?: "module";
     }
   else
     {
@@ -162,7 +151,7 @@ dwflpp::focus_on_cu(Dwarf_Die * c)
   assert(module);
 
   cu = c;
-  cu_name = default_name(dwarf_diename(c), "CU");
+  cu_name = dwarf_diename(c) ?: "CU";
 
   // Reset existing pointers and names
   function_name.clear();
@@ -181,7 +170,7 @@ dwflpp::focus_on_function(Dwarf_Die * f)
   assert(cu);
 
   function = f;
-  function_name = default_name(dwarf_diename(function), "function");
+  function_name = dwarf_diename(function) ?: "function";
 }
 
 
-- 
cgit