Replace the linear search in find_pc_sect_line with a binary search.

This patch addresses slowness when setting breakpoints, especially in
heavily templatized code. Profiling showed that find_pc_sect_line in
symtab.c was the performance bottleneck.  The original logic performed a
linear search over ordered data. This patch uses a binary search, as
suggested by comments around the function.  There are no behavioural
changes, but gdb is now faster at setting breakpoints in template code.
Tested using on make check on an x86 target. The optimisation speeds up
the included template-breakpoints.py performance test by a factor of 7
on my machine.

ChangeLog:

2018-03-20  Stephen Roberts  <stephen.roberts@arm.com>

        * gdb/symtab.c (find_pc_sect_line): now uses binary search.

gdb/testsuite/

        * gdb.perf/template-breakpoints.cc: New file.
        * gdb.perf/template-breakpoints.exp: New file.
        * gdb.perf/template-breakpoints.py: New file.
This commit is contained in:
Stephen Roberts 2018-03-20 13:54:54 +00:00
parent ed38187755
commit 4ee89e903d
6 changed files with 216 additions and 11 deletions

View File

@ -1,3 +1,7 @@
2018-03-20 Stephen Roberts <stephen.roberts@arm.com>
* gdb/symtab.c (find_pc_sect_line): now uses binary search.
2018-03-19 Tom Tromey <tom@tromey.com> 2018-03-19 Tom Tromey <tom@tromey.com>
* rust-exp.y (struct_expr_tail, struct_expr_list): Add plain * rust-exp.y (struct_expr_tail, struct_expr_list): Add plain

View File

@ -3046,8 +3046,6 @@ find_symbol_at_address (CORE_ADDR address)
find the one whose first PC is closer than that of the next line in this find the one whose first PC is closer than that of the next line in this
symtab. */ symtab. */
/* If it's worth the effort, we could be using a binary search. */
struct symtab_and_line struct symtab_and_line
find_pc_sect_line (CORE_ADDR pc, struct obj_section *section, int notcurrent) find_pc_sect_line (CORE_ADDR pc, struct obj_section *section, int notcurrent)
{ {
@ -3214,15 +3212,17 @@ find_pc_sect_line (CORE_ADDR pc, struct obj_section *section, int notcurrent)
if (item->pc > pc && (!alt || item->pc < alt->pc)) if (item->pc > pc && (!alt || item->pc < alt->pc))
alt = item; alt = item;
for (i = 0; i < len; i++, item++) auto pc_compare = [](const CORE_ADDR & pc,
{ const struct linetable_entry & lhs)->bool
/* Leave prev pointing to the linetable entry for the last line {
that started at or before PC. */ return pc < lhs.pc;
if (item->pc > pc) };
break;
prev = item; struct linetable_entry *first = item;
} struct linetable_entry *last = item + len;
item = std::upper_bound (first, last, pc, pc_compare);
if (item != first)
prev = item - 1; /* Found a matching item. */
/* At this point, prev points at the line whose start addr is <= pc, and /* At this point, prev points at the line whose start addr is <= pc, and
item points at the next line. If we ran off the end of the linetable item points at the next line. If we ran off the end of the linetable
@ -3247,7 +3247,7 @@ find_pc_sect_line (CORE_ADDR pc, struct obj_section *section, int notcurrent)
/* If another line (denoted by ITEM) is in the linetable and its /* If another line (denoted by ITEM) is in the linetable and its
PC is after BEST's PC, but before the current BEST_END, then PC is after BEST's PC, but before the current BEST_END, then
use ITEM's PC as the new best_end. */ use ITEM's PC as the new best_end. */
if (best && i < len && item->pc > best->pc if (best && item < last && item->pc > best->pc
&& (best_end == 0 || best_end > item->pc)) && (best_end == 0 || best_end > item->pc))
best_end = item->pc; best_end = item->pc;
} }

View File

@ -1,3 +1,9 @@
2018-03-20 Stephen Roberts <stephen.roberts@arm.com>
* gdb.perf/template-breakpoints.cc: New file.
* gdb.perf/template-breakpoints.exp: New file.
* gdb.perf/template-breakpoints.py: New file.
2018-03-19 Tom Tromey <tom@tromey.com> 2018-03-19 Tom Tromey <tom@tromey.com>
* gdb.rust/simple.rs (main): Add local variables field1, field2, * gdb.rust/simple.rs (main): Add local variables field1, field2,

View File

@ -0,0 +1,97 @@
/* This testcase is part of GDB, the GNU debugger.
Copyright (C) 2018 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#include <iostream>
template <int I, int J, int K, int VAL>
struct ThirdDimension
{
int
value () const
{
ThirdDimension<I, J, K - 1, VAL> d3;
return d3.value();
}
};
template <int I, int J, int VAL>
struct ThirdDimension<I, J, 0, VAL>
{
int
value () const
{
// Please note - this testcase sets a breakpoint on the following line.
// It is therefore sensitive to line numbers. If any changes are made to
// this file, please ensure that the testcase is updated to reflect this.
std::cout << "Value: " << VAL << std::endl;
return VAL;
}
};
template <int I, int J, int K, int VAL>
struct SecondDimension
{
int
value () const
{
SecondDimension<I, J - 1, K, VAL> d1;
ThirdDimension<I, J, K, VAL> d2;
return d1.value() + d2.value();
}
};
template <int I, int K, int VAL>
struct SecondDimension<I, 0, K, VAL>
{
int
value () const
{
ThirdDimension<I, 0, K, VAL> d2;
return d2.value();
}
};
template <int I, int J, int K, int VAL>
struct FirstDimension
{
int
value () const
{
FirstDimension<I - 1, J, K, VAL> d1;
SecondDimension<I, J, K, VAL> d2;
return d1.value() + d2.value();
}
};
template <int J, int K, int VAL>
struct FirstDimension<0, J, K, VAL>
{
int
value () const
{
SecondDimension<0, J, K, VAL> d2;
return d2.value();
}
};
int
main (int argc, char *argv[])
{
FirstDimension<EXPANSION_DEPTH, EXPANSION_DEPTH, EXPANSION_DEPTH, 1> product;
std::cout << product.value() << std::endl;
return 0;
}

View File

@ -0,0 +1,65 @@
# Copyright (C) 2018 Free Software Foundation, Inc.
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
# This test case is to test the performance of GDB when setting breakpoints
# on heavily temlatized C++ code.
# Parameters:
# EXPANSION_DEPTH: knob to control how many times template expansions occur
load_lib perftest.exp
if [skip_perf_tests] {
return 0
}
standard_testfile .cc
set executable $testfile
set expfile $testfile.exp
# make check-perf RUNTESTFLAGS='template-breakpoints.exp EXPANSION_DEPTH=40'
if ![info exists EXPANSION_DEPTH] {
set EXPANSION_DEPTH 40
}
PerfTest::assemble {
global EXPANSION_DEPTH
global srcdir subdir srcfile
set compile_flags {c++ debug}
lappend compile_flags "additional_flags=-DEXPANSION_DEPTH=${EXPANSION_DEPTH}"
if { [gdb_compile "$srcdir/$subdir/$srcfile" ${binfile} executable $compile_flags] != ""} {
return -1
}
return 0
} {
global binfile
clean_restart $binfile
if ![runto_main] {
fail "can't run to main"
return -1
}
return 0
} {
gdb_test "python TemplateBreakpoints().run()"
return 0
}

View File

@ -0,0 +1,33 @@
# Copyright (C) 2018 Free Software Foundation, Inc.
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
from perftest import perftest
class TemplateBreakpoints (perftest.TestCaseWithBasicMeasurements):
def __init__(self):
super (TemplateBreakpoints, self).__init__ ("template-breakpoints")
def warm_up(self):
for _ in range(0, 2):
gdb.Breakpoint("template-breakpoints.cc:38").delete()
def _do_test(self, bpcount):
for _ in range(1, bpcount):
gdb.Breakpoint("template-breakpoints.cc:38").delete()
def execute_test(self):
for bpcount in range(1, 10):
tfunc = lambda bound_bpcount=bpcount: self._do_test(bound_bpcount)
self.measure.measure(tfunc, bpcount)