This follows up MDEV-14374, which was filed against MariaDB Server 10.3.
Back then, on a 48-core Qualcomm Centriq 2400, the performance of
delay loops for spinloops was tested both with and without the dummy
compare-and-swap operation, and it was decided to keep the dummy
operation.
On target architectures where nothing special is available (other than
x86 (IA-32, AMD64) or POWER), we perform a dummy compare-and-swap operation.
This is contrary to the idea of the x86 PAUSE instruction and the
__ppc_get_timebase(), which aim to keep the memory bus idle for a while,
to allow other cores to better execute code while a spinloop is waiting
for something to be changed.
On MariaDB Server 10.4 and another implementation of the ARMv8 ISA,
omitting the dummy compare-and-swap improved performance by up to 12%.
So, let us avoid the dummy compare-and-swap on ARM.
For now, we are retaining the dummy compare-and-swap on other ISAs
(such as SPARC, MIPS, S390x, RISC-V) because we do not have any
performance data for them.
Starting with the Intel Skylake microarchitecture, the PAUSE
instruction latency is about 140 clock cycles instead of earlier 10.
On AMD processors, the latency could be 10 or 50 clock cycles,
depending on microarchitecture.
Because of this big range of latency, let us scale the loops around
the PAUSE instruction based on timing results at server startup.
my_cpu_relax_multiplier: New variable: How many times to invoke PAUSE
in a loop. Only defined for IA-32 and AMD64.
my_cpu_init(): Determine with RDTSC the time to run 16 PAUSE instructions
in two unrolled loops according, and based on the quicker of the two
runs, initialize my_cpu_relax_multiplier. This form of calibration was
suggested by Mikhail Sinyavin from Intel.
LF_BACKOFF(), ut_delay(): Use my_cpu_relax_multiplier when available.
ut_delay(): Define inline in my_cpu.h.
UT_COMPILER_BARRIER(): Remove. This does not seem to have any effect,
because in our ut_delay() implementation, no computations are being
performed inside the loop. The purpose of UT_COMPILER_BARRIER() was to
prohibit the compiler from reordering computations. It was not
emitting any code.
This commit is based on the work of Michal Schorm, rebased on the
earliest MariaDB version.
Th command line used to generate this diff was:
find ./ -type f \
-exec sed -i -e 's/Foundation, Inc., 59 Temple Place, Suite 330, Boston, /Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, /g' {} \; \
-exec sed -i -e 's/Foundation, Inc. 59 Temple Place.* Suite 330, Boston, /Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, /g' {} \; \
-exec sed -i -e 's/MA.*.....-1307.*USA/MA 02110-1335 USA/g' {} \; \
-exec sed -i -e 's/Foundation, Inc., 59 Temple/Foundation, Inc., 51 Franklin/g' {} \; \
-exec sed -i -e 's/Place, Suite 330, Boston, MA.*02111-1307.*USA/Street, Fifth Floor, Boston, MA 02110-1335 USA/g' {} \; \
-exec sed -i -e 's/MA.*.....-1307/MA 02110-1335/g' {} \;
main.derived_cond_pushdown: Move all 10.3 tests to the end,
trim trailing white space, and add an "End of 10.3 tests" marker.
Add --sorted_result to tests where the ordering is not deterministic.
main.win_percentile: Add --sorted_result to tests where the
ordering is no longer deterministic.
Part of this work is based on Stewart Smitch's memory barrier and lower priori
patches for power8.
- Added memory syncronization for innodb & xtradb for power8.
- Added HAVE_WINDOWS_MM_FENCE to CMakeList.txt
- Added os_isync to fix a syncronization problem on power
- Added log_get_lsn_nowait which is now used srv_error_monitor_thread to ensur
if log mutex is locked.
All changes done both for InnoDB and Xtradb
