Am 28.01.24 um 11:19 schrieb Bonita Montero:

A deque usually consists of a number of linear parts in memory. This
lead me to the question if scanning memory is faster forward or back-
ward. I tried to test this with the below program:

On my Windows 7050X Zen4 computer scanning memory in both directions
has the same speed. On my Linux 3990X Zen2 computer scanning forward
is 22% faster. On my small Linux PC, a HP EliteDesk Mini PC with a
Skylake Pentium G4400 scanning memory forward is about 38% faster.

I'd first have guessed that the prefetchers between the memory-levels
are as effective for both directions. So I'd like to see some results
from you.

Reverse memory access is typically slower simply because the last data
of a cache line (after a cache miss) arrives at last. If you read
forward the process continues when the first few bytes of the cache line
are read. The further data is read in parallel.

But details depend on many other factors. First of all the placement of
the memory chunks and the used prefetching technique (if any).


Marcel

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 28/01/2024 10:19, Bonita Montero wrote:

On my Windows 7050X Zen4 computer scanning memory in both directions
has the same speed. On my Linux 3990X Zen2 computer scanning forward
is 22% faster. On my small Linux PC, a HP EliteDesk Mini PC with a
Skylake Pentium G4400 scanning memory forward is about 38% faster.
I'd first have guessed that the prefetchers between the memory-levels
are as effective for both directions. So I'd like to see some results
from you.

On my Linux box with an AMD Ryzen 5 3400G it's about 11% slower for the
second number. But that's a very about, it's doing something else right
now and that's the average from several runs - where the ratio is
between 97% and 130%.

Andy

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)