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Precomputing the hash values allows us to perform more frequent
accesses to the hash table, thereby reaching higher throughputs.
We keep the old behaviour by default, since (1) we might confuse
users if they measured a speedup without changing anything in
the QHT implementation, and (2) benchmarking the hash function
"on line" is also valuable.
Before:
$ taskset -c 0 tests/qht-bench -n 1
Throughput: 38.18 MT/s
After:
$ taskset -c 0 tests/qht-bench -n 1
Throughput: 38.16 MT/s
After (with precomputing):
$ taskset -c 0 tests/qht-bench -n 1 -p
Throughput: 50.87 MT/s
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
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The meaning of "existing" is now changed to "matches in hash and
ht->cmp result". This is saner than just checking the pointer value.
Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
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qht_lookup now uses the default cmp function. qht_lookup_custom is defined
to retain the old behaviour, that is a cmp function is explicitly provided.
qht_insert will gain use of the default cmp in the next patch.
Note that we move qht_lookup_custom's @func to be the last argument,
which makes the new qht_lookup as simple as possible.
Instead of this (i.e. keeping @func 2nd):
0000000000010750 <qht_lookup>:
10750: 89 d1 mov %edx,%ecx
10752: 48 89 f2 mov %rsi,%rdx
10755: 48 8b 77 08 mov 0x8(%rdi),%rsi
10759: e9 22 ff ff ff jmpq 10680 <qht_lookup_custom>
1075e: 66 90 xchg %ax,%ax
We get:
0000000000010740 <qht_lookup>:
10740: 48 8b 4f 08 mov 0x8(%rdi),%rcx
10744: e9 37 ff ff ff jmpq 10680 <qht_lookup_custom>
10749: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
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This will enable us to decouple code translation from the value
of parallel_cpus at any given time. It will also help us minimize
TB flushes when generating code via EXCP_ATOMIC.
Note that the declaration of parallel_cpus is brought to exec-all.h
to be able to define there the "curr_cflags" inline.
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
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Every vCPU now uses a separate set of TBs for each set of dynamic
tracing event state values. Each set of TBs can be used by any number of
vCPUs to maximize TB reuse when vCPUs have the same tracing state.
This feature is later used by tracetool to optimize tracing of guest
code events.
The maximum number of TB sets is defined as 2^E, where E is the number
of events that have the 'vcpu' property (their state is stored in
CPUState->trace_dstate).
For this to work, a change on the dynamic tracing state of a vCPU will
force it to flush its virtual TB cache (which is only indexed by
address), and fall back to the physical TB cache (which now contains the
vCPU's dynamic tracing state as part of the hashing function).
Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Reviewed-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-id: 149915775266.6295.10060144081246467690.stgit@frigg.lan
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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test_start/stop are used only as flags to loop on. Barriers are unnecessary,
since no dependent data is transferred among threads apart from the flags
themselves.
This commit relaxes the three accesses to test_start/stop that were
not yet relaxed.
Signed-off-by: Emilio G. Cota <cota@braap.org>
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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This serves as a performance benchmark as well as a stress test
for QHT. We can tweak quite a number of things, including the
number of resize threads and how frequently resizes are triggered.
A performance comparison of QHT vs CLHT[1] and ck_hs[2] using
this same benchmark program can be found here:
http://imgur.com/a/0Bms4
The tests are run on a 64-core AMD Opteron 6376, pinning threads
to cores favoring same-socket cores. For each run, qht-bench is
invoked with:
$ tests/qht-bench -d $duration -n $n -u $u -g $range
, where $duration is in seconds, $n is the number of threads,
$u is the update rate (0.0 to 100.0), and $range is the number
of keys.
Note that ck_hs's performance drops significantly as writes go
up, since it requires an external lock (I used a ck_spinlock)
around every write.
Also, note that CLHT instead of using a seqlock, relies on an
allocator that does not ever return the same address during the
same read-critical section. This gives it a slight performance
advantage over QHT on read-heavy workloads, since the seqlock
writes aren't there.
[1] CLHT: https://github.com/LPD-EPFL/CLHT
https://infoscience.epfl.ch/record/207109/files/ascy_asplos15.pdf
[2] ck_hs: http://concurrencykit.org/
http://backtrace.io/blog/blog/2015/03/13/workload-specialization/
A few of those plots are shown in text here, since that site
might not be online forever. Throughput is on Mops/s on the Y axis.
200K keys, 0 % updates
450 ++--+------+------+-------+-------+-------+-------+------+-------+--++
| + + + + + + + + +N+ |
400 ++ ---+E+ ++
| +++---- |
350 ++ 9 ++------+------++ --+E+ -+H+ ++
| | +H+- | -+N+---- ---- +++ |
300 ++ 8 ++ +E+ ++ -----+E+ --+H+ ++
| | +++ | -+N+-----+H+-- |
250 ++ 7 ++------+------++ +++-----+E+---- ++
200 ++ 1 -+E+-----+H+ ++
| ---- qht +-E--+ |
150 ++ -+E+ clht +-H--+ ++
| ---- ck +-N--+ |
100 ++ +E+ ++
| ---- |
50 ++ -+E+ ++
| +E+E+ + + + + + + + + |
0 ++--E------+------+-------+-------+-------+-------+------+-------+--++
1 8 16 24 32 40 48 56 64
Number of threads
200K keys, 1 % updates
350 ++--+------+------+-------+-------+-------+-------+------+-------+--++
| + + + + + + + + -+E+ |
300 ++ -----+H+ ++
| +E+-- |
| 9 ++------+------++ +++---- |
250 ++ | +E+ -- | -+E+ ++
| 8 ++ -- ++ ---- |
200 ++ | +++- | +++ ---+E+ ++
| 7 ++------N------++ -+E+-- qht +-E--+ |
| 1 +++---- clht +-H--+ |
150 ++ -+E+ ck +-N--+ ++
| ---- |
100 ++ +E+ ++
| ---- |
| -+E+ |
50 ++ +H+-+N+----+N+-----+N+------ ++
| +E+E+ + + + +N+-----+N+-----+N+----+N+-----+N+ |
0 ++--E------+------+-------+-------+-------+-------+------+-------+--++
1 8 16 24 32 40 48 56 64
Number of threads
200K keys, 20 % updates
300 ++--+------+------+-------+-------+-------+-------+------+-------+--++
| + + + + + + + + + |
| -+H+ |
250 ++ ---- ++
| 9 ++------+------++ --+H+ ---+E+ |
| 8 ++ +H+-- ++ -+H+----+E+-- |
200 ++ | +E+ --| -----+E+-- +++ ++
| 7 ++ + ---- ++ ---+H+---- +++ qht +-E--+ |
150 ++ 6 ++------N------++ -+H+-----+E+ clht +-H--+ ++
| 1 -----+E+-- ck +-N--+ |
| -+H+---- |
100 ++ -----+E+ ++
| +E+-- |
| ----+++ |
50 ++ -+E+ ++
| +E+ +++ |
| +E+N+-+N+-----+ + + + + + + |
0 ++--E------+------N-------N-------N-------N-------N------N-------N--++
1 8 16 24 32 40 48 56 64
Number of threads
200K keys, 100 % updates qht +-E--+
clht +-H--+
160 ++--+------+------+-------+-------+-------+-------+---ck-+-N-----+--++
| + + + + + + + + ----H |
140 ++ +H+-- -+E+ ++
| +++---- ---- |
120 ++ 8 ++------+------++ -+H+ +E+ ++
| 7 ++ +H+---- ++ ---- +++---- |
100 ++ | +E+ | +++ ---+H+ -+E+ ++
| 6 ++ +++ ++ -+H+-- +++---- |
80 ++ 5 ++------N----------+E+-----+E+ ++
| 1 -+H+---- +++ |
| -----+E+ |
60 ++ +H+---- +++ ++
| ----+E+ |
40 ++ +H+---- ++
| --+E+ |
20 ++ +E+ ++
| +EE+ + + + + + + + + |
0 ++--+N-N---N------N-------N-------N-------N-------N------N-------N--++
1 8 16 24 32 40 48 56 64
Number of threads
Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <1465412133-3029-13-git-send-email-cota@braap.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>
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