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QACWRIposX90AnZMJnwxwlYMsV2t7NvylT0IGHiWh9DiMN5eo1SOYkm9fP5Yjq3EimRQlTdKt39 7aX1wkAQcm7ybvpuuk763vV9/BcufEumO/yr86RiGPWtUfvfvQwZgHQ6RmHekP4Dp0Urh7qsvF1 Jaikek4FtrPxAn3aMChZp9mtLBayZ+/+JiABrsGC3JzwL1S4TaIGBoq5MtPz3uByMYOzKmZQvPh dvVT6V3YmKnNZWlJGIPhZieAM+QjF6S0iNF4MSAht0pYZR53jUkh+Lv6s1cYyZVvR/ERaktX X-Authority-Analysis: v=2.4 cv=doDbC0g4 c=1 sm=1 tr=0 ts=687f6bed cx=c_pps a=OOZaFjgC48PWsiFpTAqLcw==:117 a=OOZaFjgC48PWsiFpTAqLcw==:17 a=6eWqkTHjU83fiwn7nKZWdM+Sl24=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=Wb1JkmetP80A:10 a=GoEa3M9JfhUA:10 a=yPCof4ZbAAAA:8 a=PE0_wtC8llDL1Pq7dcgA:9 X-Proofpoint-GUID: o8vc43zLke3CZPAI8MkSnEIIMtXeOcaa X-Proofpoint-ORIG-GUID: o8vc43zLke3CZPAI8MkSnEIIMtXeOcaa On 25 Jun 2025, eugene loh outgrape: > From: Eugene Loh > > We want to reduce the performance cost of USDT discovery if possible. > > Specifically, a number of statements -- with probe descriptions such as > "dtrace:::BEGIN" that could never specify USDT probes -- will not get > their clause flags set with DT_CLSFLAG_USDT_EXCLUDE. So these statements > get considered unnecessarily during periodic probe discovery. > > Therefore: > > *) Expand ignore_clause(dtp, n, uprp) to support the case uprp==NULL. > This case is independent of any knowledge of a specific underlying > probe. > > *) During probe discovery, check ignore_clause(dtp, i, NULL). This > sets the DT_CLSFLAG_USDT_[INCLUDE|EXCLUDE] flag and allows faster > exclusion of statements that do not need to be reconsidered. I'm pretty amazed you can even detect this optimization, but the code change feels like a good idea anyway, if just on code reuse grounds. > To take advantage of this optimization, users should specify providers. > E.g., instead of "BEGIN" (which could conceivably be a USDT probe), > specify "dtrace:::BEGIN". It's a shame this is necessary though. (In practice, nobody is ever going to do it for BEGIN, at least -- but it's common enough with other probes to be worth taking advantage of.) > Signed-off-by: Eugene Loh Reviewed-by: Nick Alcock modulo the tiny nit below. > - char lastchar = pdp->prv[len - 1]; > + char lastchar = (pdp->prv[0] != '\0' ? pdp->prv[len - 1] : '*'); I'd be a bit more belt-and-braces here, given that if this goes wrong it's a buffer overrun: > + char lastchar = ((pdp->prv[0] != '\0' && len > 0) ? pdp->prv[len - 1] : '*'); > @@ -555,6 +559,8 @@ ignore_clause(dtrace_hdl_t *dtp, int n, const dt_probe_t *uprp) > } > if (dt_stmt_clsflag_test(stp, DT_CLSFLAG_USDT_EXCLUDE) == 1) > return 1; > + if (uprp == NULL) > + return 0; This could do with a blank line above the first if in this hunk, I think? > > /* > * If we cannot ignore this statement, try to use uprp. > @@ -751,13 +757,9 @@ static int discover(dtrace_hdl_t *dtp) > */ > memset(&pcb, 0, sizeof(dt_pcb_t)); > for (i = 0; i < dtp->dt_stmt_nextid; i++) { > - dtrace_stmtdesc_t *stp; > - > - stp = dtp->dt_stmts[i]; > - if (stp == NULL) > + if (ignore_clause(dtp, i, NULL)) > continue; > - if (dt_stmt_clsflag_test(stp, DT_CLSFLAG_USDT_EXCLUDE) != 1) > - dt_pid_create_usdt_probes(&stp->dtsd_ecbdesc->dted_probe, dtp, &pcb); > + dt_pid_create_usdt_probes(&dtp->dt_stmts[i]->dtsd_ecbdesc->dted_probe, dtp, &pcb); (straight moves into the callee, ok.) -- NULL && (void)