From: Josh Stone <jistone@redhat.com>
Date: Mon, 8 Jun 2009 22:36:42 +0000 (-0700)
Subject: Let query_module abort early for simple matches
X-Git-Tag: release-0.9.8~19
X-Git-Url: https://sourceware.org/git/?a=commitdiff_plain;h=0e14e0793ffb891bccd465cf518480685e3cd49e;p=systemtap.git

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.
---

diff --git a/dwflpp.cxx b/dwflpp.cxx
index 3af260536..1a5897713 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.
diff --git a/tapsets.cxx b/tapsets.cxx
index 50e80cf5b..d8fe8f8ea 100644
--- a/tapsets.cxx
+++ b/tapsets.cxx
@@ -1776,13 +1776,13 @@ query_module (Dwfl_Module *mod,
       // If we have enough information in the pattern to skip a module and
       // the module does not match that information, return early.
       if (!q->dw.module_name_matches(q->module_val))
-        return DWARF_CB_OK;
+        return pending_interrupts ? DWARF_CB_ABORT : DWARF_CB_OK;
 
       // Don't allow module("*kernel*") type expressions to match the
       // elfutils module "kernel", which we refer to in the probe
       // point syntax exclusively as "kernel.*".
       if (q->dw.module_name == TOK_KERNEL && ! q->has_kernel)
-        return DWARF_CB_OK;
+        return pending_interrupts ? DWARF_CB_ABORT : DWARF_CB_OK;
 
       if (mod)
         validate_module_elf(mod, name, q);
@@ -1810,7 +1810,7 @@ query_module (Dwfl_Module *mod,
 
 
       // If we know that there will be no more matches, abort early.
-      if (q->dw.module_name_final_match(q->module_val))
+      if (q->dw.module_name_final_match(q->module_val) || pending_interrupts)
         return DWARF_CB_ABORT;
       else
         return DWARF_CB_OK;