Avoid using atomics as it_wait is guarded by td_lock.
Report threshold calculation is done only if at least one PMC hook
is installed
- there will be another patch with pmc.soft(3) update
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mjg kib mhorne - Commits
- rG7bc13692a2d6: hwpmc: fix performance issues
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You should always modify the conter, but only do branch on stuff depending on PMC_HOOK_INSTALLED_ANY
| sys/kern/kern_intr.c | ||
|---|---|---|
| 1026 | the point was to avoid needing to read intr_hwpmc_waiting_report_threshold if hwpmc is not loaded. So this should be: it->it_waiting++;
if (PMC_HOOK_INSTALLED_ANY()) {
if (it->it_waiting >= intr_hwpmc_waiting_report_threshold) {
PMC_SOFT_CALL_INTR_HLPR(waiting, frame);
}
}.or so | |
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OK, so if I got your point, you meant
- avoid unnecessary branching (if frame != null ...) by having PMC_HOOK_INSTALLED_ANY condition on the top of them, which should hint the core not to execute speculatively anything which us underneath;
- access intr_hwpmc_waiting_report_threshold cacheline only if at least one hook is loaded;
right?