On 8/21/19 1:50 PM, Bill Somerville wrote:
Many thanks, Bill, for this interesting and comprehensive information.
Best wishes,
Claude (DJ0OT)
the first thing you must do is to check you are comparing like with
like. The FTol parameter has a major bearing on the consumption of CPU
resource in MSK144 reception mode, unless you are comparing performance
between versions using the same value for FTol you are not doing a valid
test.
With respect to the performance advantage of using a 64-bit instruction
set, the considerably larger number of general purpose CPU registers
allows compilers to emit more efficient code where values in registers
are not having to be copied to RAM and back to free registers for other
computations (register spills), this can have a significant advantage in
CPU bound algorithms like the MSK144 decoder. I believe there is also
some advantage in that the emulation of 32-bit instructions on a 64-bit
processor is not cost free compared with running the same code on a
32-bit processor. The extra address space when using a 64-bit processor
is not particularly beneficial to WSJT-X, although on a machine running
many processes, hard memory page faults are less likely if all processes
can have more of their memory pages in physical memory. Extra unused
physical memory addressable in a 64-bit processor system should be used
by the operating system for file cacheing and that in turn will speed up
disk I/O bound processes, possibly freeing up CPU resource to other CPU
bound processes.
With respect to Qt5, there are not really any routines in WSJT-X that
are CPU bound while using Qt code. The parts running Qt code are
virtually all I/O bound mostly waiting for user input or updating the
display in response to I/O based events.
On the recently revealed, and mostly mitigated, vulnerabilities you
mention; they are in the domain of the operating system kernel rather
than the BIOS or firmware until the real fix via newer processor
generations are adopted (9th generation "Coffee Lake" in the case of
Intel Core CPUs). The kernel mitigations involve some level of
pessimization with the slow down being greatest on the oldest processor
models, expected performance impacts of mitigations are between 30% down
to as low as 2% on newer CPUs like the 8th generation "Coffee Lake"
Intel Core CPUs.
73
Bill
G4WJS.
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