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Dear SystemTap developers, I noticed that compile time for a non-cached module greatly increased since SystemTap snapshot 20070721. On my system (RHEL4 with 2.6.25 kernel; dual Intel Xeon(TM) CPU 2.80GHz with HT; 5 GB RAM), phase 2 takes about half an hour to complete. This problem also occurs in SystemTap 0.8 and in most recent snapshots. Using strace, I found that stap spends most of time for generating the header "stap-symbols.h" in function dump_unwindsyms() (in translate.cxx). Here it is the "guilty" code: // Add unwind data to be included if it exists for this module. size_t len = 0; void *unwind = get_unwind_data (m, &len); if (unwind != NULL) { c->output << "#ifdef STP_USE_DWARF_UNWINDER" << endl; c->output << "static uint8_t _stp_module_" << stpmod_idx << "_unwind_data[] = " << endl; c->output << " {"; for (size_t i = 0; i < len; i++) { int h = ((uint8_t *)unwind)[i]; c->output << "0x" << hex << h << dec << ","; if ((i + 1) % 16 == 0) c->output << endl << " "; } c->output << "};" << endl; c->output << "#endif /* STP_USE_DWARF_UNWINDER */" << endl; } and for (unsigned secidx = 0; secidx < seclist.size(); secidx++) { c->output << "struct _stp_symbol " << "_stp_module_" << stpmod_idx<< "_symbols_" << secidx << "[] = {" << endl; // We write out a *sorted* symbol table, so the runtime doesn't have to sort them later. for (addrmap_t::iterator it = addrmap[secidx].begin(); it != addrmap[secidx].end(); it++) { if (it->first < extra_offset) continue; // skip symbols that occur before our chosen base address c->output << " { 0x" << hex << it->first-extra_offset << dec << ", " << lex_cast_qstring (it->second) << " }," << endl; } c->output << "};" << endl; } As far as I know, the "stap-symbols.h" file contains the list of kernel symbols (preliminarly ordered by name) in order to speed-up symbol resolution at run-time. Because the symbol list remains the same if the kernel is unchanged, I think that stap-symbols.h should be cached in order to speed up phase 2. You can find a very simple patch I made on SystemTap 0.8 which caches stap-symbols.h into ~/.systemtap (it only takes into account the modification time of /boot/vmlinux-VERSION, so it can be greatly improved). Please consider the addition of caching mechanisms for stap-symbols.h in future releases of SystemTap. Thank you for your support Roberto Natella
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