On SMT systems, empty spinloops can cause excessive latency due to
the spinning core consuming resources that could be used by other
hardware threads. This series addresses this by adding rte_pause()
calls to busy-wait loops in the cnxk drivers.
The first two patches fix existing empty spinloops in the net/cnxk
and event/cnxk drivers. These were identified using a new coccinelle
script that finds variations of the pattern:
while (!atomic(&flag));
This is compile tested only! I don't have that hardware.
The third patch adds this coccinelle script to devtools/ so that
similar issues can be detected and fixed automatically across the
codebase.
The script handles multiple atomic API variants:
- Legacy rte_atomic*_read() functions
- C11 atomics via rte_atomic_load_explicit()
- GCC builtins via __atomic_load_n()
- Simple volatile variable checks
Stephen Hemminger (3):
net/cnxk: add pause to spinloops
event/cnxk: add pause to spinloops
devtools/cocci: add script to find empty spinloops
devtools/cocci/fix_empty_spinloops.cocci | 165 +++++++++++++++++++++++
drivers/event/cnxk/cn10k_worker.c | 2 +-
drivers/event/cnxk/cn20k_worker.c | 2 +-
drivers/event/cnxk/cnxk_tim_worker.h | 4 +-
drivers/net/cnxk/cn10k_tx.h | 4 +-
drivers/net/cnxk/cn20k_tx.h | 4 +-
6 files changed, 173 insertions(+), 8 deletions(-)
create mode 100644 devtools/cocci/fix_empty_spinloops.cocci
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2.51.0
