Benchmark automation - TCWG-360 [3/10]
* Created a partial Jenkins prototype
* Considered some security issues
Benchmarking presentation [5/10]
* Drafted some slides, did some reading
Misc [2/10]
=Plan=
More of the above
== Progress ==
* TCWG-849 (1/10)
- Committed improvement for VRP
https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=225108
* Add REG_EQUAL for arm_emit_movpair (4/10)
- Posted patches for review
* TACT -TCWG-851 (3/10)
- Started with the small examples.
- Ran into an error while tuning; looking into it
* Git work flow for upstream patches -TCWG-848 (1/10)
- Had a chat with Michael and Prathamesh
- Tried the work-flow and now started documenting them
* Misc (1/10)
- gcc-patches, gcc-bugs list
- Meetings
== Plan ==
- GCC Bugs
- TACT driven optimization exploration for gcc
* TCWG-830 (4/10)
- Observing tree dumps
- Peeling for alignment happens at -O3 but not at -O2 -ftree-vectorize
Reason: in vect_enhance_data_refs_alignment() for:
a) -O2 -ftree-vectorize: max_allowed_peel == 0
b) -O3: max_allowed_peel == (unsigned) -1;
which equals UINT_MAX and therefore peeling gets allowed.
- Workaround: Pass -param vect-max-peeling-for-alignment=0
- Peeling for alignment with O2 can be enabled by passing
-fvect-cost-model (we don't want this!)
Reason:
opts.c:
/* Tune vectorization related parametees according to cost model. */
if (opts->x_flag_vect_cost_model == VECT_COST_MODEL_CHEAP)
{
maybe_set_param_value (PARAM_VECT_MAX_VERSION_FOR_ALIAS_CHECKS,
6, opts->x_param_values, opts_set->x_param_values);
maybe_set_param_value (PARAM_VECT_MAX_VERSION_FOR_ALIGNMENT_CHECKS,
0, opts->x_param_values, opts_set->x_param_values);
maybe_set_param_value (PARAM_VECT_MAX_PEELING_FOR_ALIGNMENT,
0, opts->x_param_values, opts_set->x_param_values);
}
The above if condition becomes false when -fvect-cost-model is passed.
- Proposed patch (untested): http://pastebin.com/ftp0mrwH
Patch follows the workaround and passes --param vect-max-peeling-for-alignment=0
if unaligned access is supported.
* TCWG-777 (4/10)
- Observing tree and rtl dumps
- Workaround: for -O1 pass -fno-tree-fre -fno-tree-dominator-opts
Test-case: http://pastebin.com/cjBcSpiT
Generated assembly at -O1 without workaround: http://pastebin.com/jmQGZhN9
Generated assembly at -O1 with workaround: http://pastebin.com/JGj05z66
Is that the expected output for no unnecessary temps in assembly with
workaround ?
Is it profitable over the assembly generated without workaround ?
- Approach currently taken:
a) New pass "remove-temps" (for lack of better name), after nrv (added
as last gimple pass).
b) Transforms:
if (ssa_var != 0)
to
new_ssa_var = SSA_NAME_DEF_STMT (ssa_var)
if (new_ssa_var != 0)
This "unfolds" cse on expressions within if, which was done by fre
(and if fre was disabled then by dom pass).
c) However this approach results in dead stores.
eg:
_8 = flags_7(D) & 1;
if (_8 != 0)
...
is transformed to:
_8 = flags_7(D) & 1;
_32 = flags_7(D) & 1;
if (_32 != 0)
...
so store to _8 is dead store.
I tried to run dse after remove-temps but that didn't work.
RTL 194r.jump eliminates the above dead store as "trivially dead insn".
However I don't think it's a good idea to have dead stores like these
in gimple and rely
on RTL to eliminate them. I could try to make the pass bit smarter to
not generate redundant stores like _32 != 0 in above case.
d) Patch (no intent to commit as-is): http://pastebin.com/AGXnSkrZ
Generated assembly at -O1 with the patch: http://pastebin.com/VmHCVpGC
Patch eliminates temporaries at -O1 but not at -O2.
I have not yet figured out the reason for that.
For if (flags & 1),
In dfinish pass for -O1, the generated RTL is from
zeroextractsi_compare0_scratch
while for -O2, the generated RTL is from andsi3_compare0
e) Is this a problem also on x86 ?
x86 generated assembly with -O1: http://pastebin.com/XMeTXXwK
* Misc (2/10)
- Getting familiar with vectorizer and NEON gcc intrinsics
- Reviewed git tutorials and starting preparation of git doc
- Conference calls
== Next Week ==
- Continue working on TCWG-830 and TCWG-777
- Header file flattening
- Travel to Mumbai on 2nd July (Thursday) for US Visa OFC appointment.
== Progress ==
* Maintenance (CARD-1833 4/10)
- Found the trail on the ADD/SUB with negative immediate
- Submitting RFC for discussion (http://llvm.org/PR20978)
- Bugzilla farming
- More LNT investigations (http://llvm.org/perf/ unstable)
* Releases (CARD-1431 1/10)
- Building, testing and uploading 3.6.2 RC1
* Background (5/10)
- Code review, meetings, discussions, etc.
- More stride vectorizer code review (lnN/stN implementation)
- More lab discussions (routers, lab split, new link)
- Changing my dev env to emacs (huge mind set flip)
== Plan ==
* Continue with ADD/SUB change
* Continue with Emacs setup
* Move benchmark bot to CMake
* Some other bugs
* One day off on Thu [2/10]
# Progress #
* Linaro GDB [4/10]
** TCWG-805, aarch64 native debugging multi-arch support.
Prepare for the patches submission.
It is a big patch series, and think about how to upstream them.
Write commit log including the rationale of the changes.
* FSF GDB [2/10]
** FSF GDB 7.10 release. Audit some GDB regressions caused by intel
mpx stuff.
** PR 18605. Write a patch and it is in testing.
** Other patches review.
* Misc [2/10]
** File expense report for Grenoble travel.
** Some discussions on aarch64 tracepoint.
# Plan #
* TCWG-805, upstream some patches on multi-arch debugging.
--
Yao
* One day off (Wed) (2/10)
== Progress ==
* linaro-5.1-2015.06 snapshot (1/10)
- dealt with tags, release notes
- shared it with B&B
* 4.8-2015.06 branch merge (1/10)
- investigated regression: incorrect automatic merge
- fixed, validation on-going
* 4.9 branch (2/10)
- updated our git linaro-4.9-branch to match the svn one
- ready for branch merge, will be done right after fsf release
* Misc (4/10)
- meetings, conf-calls, emails, reviews (GCC backports, ABE, backflip)
== Next ==
* more reviews for new backports
* backports, release, validation: update doc
* hopefully upstream work
Recently I came across two excellent post about accelerating clang/llvm
build with different compiler/optimization [1] [2].
I tried some of author advices getting very good results. Basically I
moved to optimized clang build, changed to gold linker and used another
memory allocator than system glibc one. Results in build time for all
the clang/llvm toolchain is summarized below (my machine is a i7-4510U,
2C/4T, 8GB, 256GB SSD):
GCC 4.8.4 + gold (Ubuntu 14.04)
real 85m17.640s
user 257m1.976s
sys 11m35.284s
LLVM 3.6 + gold (Ubuntu 14.04)
real 34m4.909s
user 128m43.382s
sys 3m51.643s
LLVM 3.7 + gold + tcmalloc
real 32m56.707s
user 121m40.562s
sys 3m52.358s
Gold linker also shows a *much* less RSS usage, I am able to fully use make -j4
while linking in 8GB without issue any swapping.
Two things I would add/check for the posts:
1. Change from libc to tcmalloc showed me a 3-4% improvement. I tried jemalloc,
but tcmalloc is faster. I am using currently system version 2.2, but I have
pushed an aggressive decommit patch to enable as default for 2.4 that might
show lower RSS and latency (I will check it later).
2. First I try to accelerate my build by offloading compilation using distcc.
Results were good, although the other machine utilization (i7, 4C/8T, 8GB)
showed mixes cpu utilization. The problem was linking memory utilization
using ld.bfd, which generates a lot of swapping with higher job count. I
will try using distcc with clang.
[1] http://blogs.s-osg.org/an-introduction-to-accelerating-your-build-with-clan…
[2] http://blogs.s-osg.org/a-conclusion-to-accelerating-your-build-with-clang/
Benchmark automation - TCWG-360 [7/10]
* Arndales stopped booting
** Package servers for elderly filesystem had gone
** Investigated some approaches to creating more stable filesystems
** Realized I could just updated image to point at old-releases, so
did that for now
* _More_ time thinking about interactions with Jenkins & LAVA. Fathi
gave me some Jenkins jobs to prototype in.
* Brain-dumped some of the present state of things into Collaborate
Misc - [3/10]
=Plan=
Jenkins prototyping
>> Using Python to script GDB makes it much more efficient to do testing.
>> Having a Python-disabled build of GDB prevents this.
I use the example of the gdb-python scripts for the linux kernel.
They are very useful, these do not work when using GDB from windows.
-Duane
It seems the prebuilt windows releases of GDB do not enable Python.
Are there plans to release a python-enabled-gdb in the windows builds?
If not, what are the roadblocks to this?
Thanks
Example:
$ ./aarch64-linux-gnu-gdb.exe
GNU gdb (Linaro GDB 2015.02-3) 7.8-2014.09-1-git
Copyright (C) 2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later
<http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show
copying"
and "show warranty" for details.
This GDB was configured as "--host=i686-w64-mingw32
--target=aarch64-linux-gnu"
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<https://bugs.launchpad.net/gcc-linaro>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word".
(gdb) python
>
>Scripting in the "Python" language is not supported in this copy of GDB.
(gdb) quit
