On 9/12/21 06:03, Jens Axboe wrote:
On 9/11/21 9:19 PM, Bart Van Assche wrote:
The performance numbers in the patch description come from a
Intel Xeon Gold 6154 CPU. I reran the test today on an old Intel
Core i7-4790 CPU and obtained the opposite result: higher IOPS
without this patch than with this patch although the assembler
code looks to be the same. It seems like how fast "rep stos"
runs depends on the CPU type?
It does appear so. Which is a bit frustrating...
Further measurements have shown that this behavior is specific to
gcc and also that clang always generates faster code for the version
of bio_init() in my patch. I have reported this as a bug to the gcc
project. See also https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102294.
Bart.
