In 06c4cc3660, we split the multiplication in two parts to avoid
a clang warning. But because double still rounds to 53 bits, this
does not provide additional precision beyond multiplication by
nextafter(0x1p64, 0), the largest representable value smaller
than 2**64.
However, since we have eliminated 1.0, mutiplying by 2**64 produces
a better distribution of input values to the output values.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200626200950.1015121-3-richard.henderson@linaro.org>
Since the seed must be non-zero, subtracting 1 means puts the
rate in 0..UINT64_MAX-1, which allows the 0 and UINT64_MAX
thresholds to corrspond to 0% (never) and 100% (always).
Suggested-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200626200950.1015121-2-richard.henderson@linaro.org>
tests/qht-bench.c:287:29: error: implicit conversion from 'unsigned long'
to 'double' changes value from 18446744073709551615
to 18446744073709551616 [-Werror,-Wimplicit-int-float-conversion]
*threshold = rate * UINT64_MAX;
~ ^~~~~~~~~~
Fix this by splitting the 64-bit constant into two halves,
each of which is individually perfectly representable, the
sum of which produces the correct arithmetic result.
This is very likely just a sticking plaster over some underlying
incorrect code, but it will suppress the warning for the moment.
Cc: Emilio G. Cota <cota@braap.org>
Reported-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Relying on sleep to always return having slept isn't safe as a signal
may have occurred. If signals are constantly incoming the program will
never reach its termination condition. This is believed to be the
mechanism causing time outs for qht-test in Travis.
The glib g_usleep() deals with all of this for us so lets use it instead.
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@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>
Before moving them all to include/qemu/xxhash.h.
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>
Which we forgot to do in bd224fce60 ("qht-bench: add -p flag
to precompute hash values", 2018-09-26).
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>
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>
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>
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>
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>
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>
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>
