On 1/17/25 08:17, H. Peter Anvin wrote:
- switch (regs->fred_ss.type) {
+ switch_likely (etype, (EVENT_TYPE_EXTINT == etype ||
EVENT_TYPE_OTHER == etype)) {
This is not what I suggested, the (l) argument should be only one
constant; __builtin_expect() doesn't allow 2 different constants.
The (l) argument is not a boolean expression! It is the *expected value*
of (v).
Also, EVENT_TYPE_EXTINT == etype is not Linux style.
More fundamentally, though, I have to question this unless based on
profiling, because it isn't at all clear that EXTINT is more important
than FAULT (page faults, to be specific.)
To optimize syscalls, you want to do a one-shot comparison of the entire
syscall64 signature (event type, 64-bit flag, and vector) as a mask and
compare. For that you want to make sure the compiler loads the high 32
bits into a register so that your mask and compare values can be
immediates. In other words, you don't actually want it to be part of the
switch at all, and you want *other* EVENT_TYPE_OTHER to fall back to the
switch with regular (low) priority.
-hpa
