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5 Commits

Author SHA1 Message Date
Emilio G. Cota
7d0440dec4
tb-hash: improve tb_jmp_cache hash function in user mode 
Optimizations to cross-page chaining and indirect branches make
performance more sensitive to the hit rate of tb_jmp_cache.
The constraint of reserving some bits for the page number
lowers the achievable quality of the hashing function.

However, user-mode does not have this requirement. Thus,
with this change we use for user-mode a hashing function that
is both faster and of better quality than the previous one.

Measurements:

Note: baseline (i.e. speedup == 1x) is QEMU v2.9.0.

- SPECint06 (test set), x86_64-linux-user. Host: Intel i7-6700K @ 4.00GHz

2.2x +-+--------------------------------------------------------------------------------------------------------------+-+
| |
| jr |
2x +jr+multhash +....................................................+++++...................................+-+
| jr+hash |$$$ |
| |$+$ |
| ### $ |
1.8x +-+......................................................................#|#.$...................................+-+
| ++#+# $ |
| |# # $ |
1.6x +-+....................................................................***.#.$....................++$$$..........+-+
| $$$ *+* # $ |$+$ |
| ++$$$ ### $ * * # $ +++|$ $ |
| ++###+$ # # $ * * # $ ### ****## $ |
1.4x +-+...................***+#.$.........***.#.$..........................*.*.#.$...........#+#$$.*++*|#.$..........+-+
| *+* # $ * * # $ * * # $ # # $ * *+# $ |
| * * # $ +++++ * * # $ * * # $ *** # $ * * # $ ###$$ |
1.2x +-+...................*.*.#.$.***##$$.*.*.#.$..........................*.*.#.$.........*.*.#.$.*..*.#.$.***+#+$..+-+
| * * # $ *+* # $ * * # $ +++ * * # $ ++###$$ * * # $ * * # $ * * # $ |
| ***##$$ * * # $ * * # $ * * # $ ***##$$ ++### * * # $ *** #+$ * * # $ * * # $ * * # $ |
| *+*+#+$ ***##$$$ * * # $ * * # $ * * # $ *+* # $ ++####$$ ***+# * * # $ * * # $ * * # $ * * # $ * * # $ |
1x +-++-*+*+#+$+*+*+#-+$+*+*-#+$+*+*+#+$+*+*+#+$+*-*+#+$+***++#+$+*+*+#$$+*+*+#+$+*+*+#+$+*+*-#+$+*+-*+#+$+*+*+#+$-++-+
| * * # $ * * # $ * * # $ * * # $ * * # $ * * # $ * * # $ * * # $ * * # $ * * # $ * * # $ * * # $ * * # $ |
| * * # $ * * # $ * * # $ * * # $ * * # $ * * # $ * * # $ * * # $ * * # $ * * # $ * * # $ * * # $ * * # $ |
0.8x +-+--***##$$-***##$$$-***##$$-***##$$-***##$$-***##$$-***###$$-***##$$-***##$$-***##$$-***##$$-****##$$-***##$$--+-+
astar bzip2 gcc gobmk h264ref hmmlibquantum mcf omnetpperlbench sjengxalancbmk hmean
png: http://imgur.com/4UXTrEc

Here I also tried the hash function suggested by Paolo ("multhash"):

return ((uint64_t) (pc * 2654435761) >> 32) & (TB_JMP_CACHE_SIZE - 1);

As you can see it is just as good as the other new function ("hash"),
which is what I ended up going with.

- SPECint06 (train set), x86_64-linux-user. Host: Intel i7-6700K @ 4.00GHz

2.6x +-+--------------------------------------------------------------------------------------------------------------+-+
| |
| jr ### |
2.4x +jr+hash...........................................................................................#.#...........+-+
| # # |
| # # |
2.2x +-+................................................................................................#.#...........+-+
| # # |
| # # |
2x +-+................................................................................................#.#...........+-+
| **** # |
| * * # |
1.8x +-+.............................................................................................*..*.#...........+-+
| +++ * * # |
| #### #### * * # |
1.6x +-+......................................####.............................#..#.****..#..........*..*.#...........+-+
| +++ #++# **** # * * # #### * * # |
| ### # # * * # * * # # # * * # |
1.4x +-+...................****+#..........****..#..........................*..*..#.*..*..#....#..#..*..*.#...........+-+
| *++* # * * # * * # * * # *** # * * # #### |
| * * # #### * * # * * # * * # * * # * * # **** # |
1.2x +-+...................*..*.#..****++#.*..*..#..........................*..*..#.*..*..#..*.*..#..*..*.#..*..*..#..+-+
| ****### * * # * * # * * # * * # * * # * * # * * # * * # |
| * * # ***### * * # * * # * * # ****## * * # * * # * * # * * # * * # |
1x +-+--****###--***###--****##--****###-****###--***###--***###--****##--****###-****###--***###--****##--****###--+-+
astar bzip2 gcc gobmk h264ref hmmlibquantum mcf omnetpperlbench sjengxalancbmk hmean
png: http://imgur.com/ArCbHqo

- NBench, x86_64-linux-user. Host: Intel i7-6700K @ 4.00GHz

1.12x +-+-------------------------------------------------------------------------------------------------------------+-+
| |
| jr +++ |
1.1x +jr+hash...........................................................####.........................................+-+
| +++#| # |
| | #++# |
1.08x +-+................................+++................+++.+++..*****..#.........................................+-+
| | +++ | | * | * # |
| | | | | *+++* # |
1.06x +-+................................****###.............|...|...*...*..#.........................+++.............+-+
| *| * |# ****### * * # | |
| *| *++# *| * |# * * # #### |
1.04x +-+................................*++*..#............*|.*.|#..*...*..#........................#.|#.............+-+
| * * # *++*++# * * # +++#++# |
| * * # * * # * * # | # # +++#### |
1.02x +-+................................*..*..#......+++...*..*..#..*...*..#.....................****..#..*****++#...+-+
| +++ * * # +++ | * * # * * # +++ *| * # *+++* # |
| +++ | +++ +++ ++++++ * * # *****### * * # * * # | +++ ++++++ *++* # * * # |
1x +-++-+++++####++****###++++-+####+-*++*++#-+*+++*-+#++*++*++#++*+-+*++#+-+++####-+*****###++*++*++#++*+-+*++#+-++-+
| *****| # *++* |# *****| # * * # * *++# * * # * * # **** |# * * # * * # * * # |
| * | *| # * *++# * | *++# * * # * * # * * # * * # *| *++# * * # * * # * * # |
0.98x +-+...*.|.*++#..*..*..#..*+++*..#..*..*..#..*...*..#..*..*..#..*...*..#..*++*..#..*...*..#..*..*..#..*...*..#...+-+
| *+++* # * * # * * # * * # * * # * * # * * # * * # * * # * * # * * # |
| * * # * * # * * # * * # * * # * * # * * # * * # * * # * * # * * # |
0.96x +-+---*****###--****###--*****###--****###--*****###--****###--*****###--****###--*****###--****###--*****###---+-+
ASSIGNMENT BITFIELD FOURFP EMULATION HUFFMAN LU DECOMPOSITIONEURAL NNUMERIC SOSTRING SORT hmean
png: http://imgur.com/ZXFX0hJ

- NBench, arm-linux-user. Host: Intel i7-4790K @ 4.00GHz

1.3x +-+-------------------------------------------------------------------------------------------------------------+-+
| #### |
| jr # # +++ |
1.25x +jr+hash.....................#..#...........................................####................................+-+
| # # # # |
| # # # # |
1.2x +-+..........................#..#...........................................#..#................................+-+
| # # # # |
| # # # # |
1.15x +-+..........................#..#...........................................#..#................................+-+
| # # #### # # |
| # # # # # # |
1.1x +-+..........................#..#..................................#..#.....#..#................................+-+
| # # # # # # +++ |
| # # #### # # # # #### |
1.05x +-+..........................#..#...............#..#.....####......#..#.....#..#.........................#..#...+-+
| # # # # # # # # # # +++ # # |
| +++ ***** # #### ***** # # # +++# # **** # ****### # # |
1x +-++-+*****###++****+++++*+-+*++#+-****++#-+*+++*-+#+++++#++#++*****++#+-*++*++#-+*****-++++*++*++#++*****++#+-++-+
| * * # * * | * * # * * # * * # **** # * * # * * # * *### * *++# * * # |
| * * # * *### * * # * * # * * # * * # * * # * * # * * # * * # * * # |
0.95x +-+...*...*..#..*..*.|#..*...*..#..*..*..#..*...*..#..*..*..#..*...*..#..*..*..#..*...*..#..*..*..#..*...*..#...+-+
| * * # * * |# * * # * * # * * # * * # * * # * * # * * # * * # * * # |
| * * # * * |# * * # * * # * * # * * # * * # * * # * * # * * # * * # |
0.9x +-+---*****###--****###--*****###--****###--*****###--****###--*****###--****###--*****###--****###--*****###---+-+
ASSIGNMENT BITFIELD FOURFP EMULATION HUFFMAN LU DECOMPOSITIONEURAL NNUMERIC SOSTRING SORT hmean
png: http://imgur.com/FfD27ey

Backports commit 6f1653180f5701c6a8f1b35b89a80b1e3260928e from qemu
 2018-03-03 14:11:29 -05:00
Markus Armbruster
1275b9b459
Clean up ill-advised or unusual header guards 
Cleaned up with scripts/clean-header-guards.pl.

Backports commit 2a6a4076e117113ebec97b1821071afccfdfbc96 from qemu
 2018-02-25 04:22:46 -05:00
Emilio G. Cota
ae3e22a689
tb hash: hash phys_pc, pc, and flags with xxhash 
For some workloads such as arm bootup, tb_phys_hash is performance-critical.
The is due to the high frequency of accesses to the hash table, originated
by (frequent) TLB flushes that wipe out the cpu-private tb_jmp_cache's.
More info:
https://lists.nongnu.org/archive/html/qemu-devel/2016-03/msg05098.html

To dig further into this I modified an arm image booting debian jessie to
immediately shut down after boot. Analysis revealed that quite a bit of time
is unnecessarily spent in tb_phys_hash: the cause is poor hashing that
results in very uneven loading of chains in the hash table's buckets;
the longest observed chain had ~550 elements.

The appended addresses this with two changes:

1) Use xxhash as the hash table's hash function. xxhash is a fast,
high-quality hashing function.

2) Feed the hashing function with not just tb_phys, but also pc and flags.

This improves performance over using just tb_phys for hashing, since that
resulted in some hash buckets having many TB's, while others getting very few;
with these changes, the longest observed chain on a single hash bucket is
brought down from ~550 to ~40.

Tests show that the other element checked for in tb_find_physical,
cs_base, is always a match when tb_phys+pc+flags are a match,
so hashing cs_base is wasteful. It could be that this is an ARM-only
thing, though. UPDATE:
On Tue, Apr 05, 2016 at 08:41:43 -0700, Richard Henderson wrote:
> The cs_base field is only used by i386 (in 16-bit modes), and sparc (for a TB
> consisting of only a delay slot).
> It may well still turn out to be reasonable to ignore cs_base for hashing.

BTW, after this change the hash table should not be called "tb_hash_phys"
anymore; this is addressed later in this series.

This change gives consistent bootup time improvements. I tested two
host machines:
- Intel Xeon E5-2690: 11.6% less time
- Intel i7-4790K: 19.2% less time

Increasing the number of hash buckets yields further improvements. However,
using a larger, fixed number of buckets can degrade performance for other
workloads that do not translate as many blocks (600K+ for debian-jessie arm
bootup). This is dealt with later in this series.

Backports commit 42bd32287f3a18d823f2258b813824a39ed7c6d9 from qemu
 2018-02-24 18:00:14 -05:00
Peter Crosthwaite
82a22d8f3a
cpu-defs: Move out TB_JMP defines 
These are not Architecture specific in any way so move them out of
cpu-defs.h. tb-hash.h is an appropriate place as a leading user and
their strong relationship to TB hashing and caching.

Backports commit 41da4bd6420afd1209c408974920f63ff9c658e1 from qemu
 2018-02-17 15:23:15 -05:00
Peter Crosthwaite
09d23c6604
include/exec: Move tb hash functions out 
This is one of very few things in exec-all with a genuine CPU
architecture dependency. Move these hashing helpers to a new
header to trim exec-all.h down to a near architecture-agnostic
header.

The defs are only used by cpu-exec and translate-all which are both
arch-obj's so the new tb-hash.h has no core code usage.

Backports commit e1b89321bafea9fb33d87852fc91fee579d17dfe from qemu
 2018-02-17 15:23:15 -05:00