clayborg requested changes to this revision. clayborg added a comment. This revision now requires changes to proceed.
In https://reviews.llvm.org/D32757#743567, @scott.smith wrote: > IMO, this is a simpler interface than TaskRunner. Also, after this, there > are no users of TaskRunner left. Should I just delete them? I think you might not have understood TaskRunner's real benefits. It is smart in the way it runs things: it lets you run N things and get each item **as soon as it completes**. The TaskMap will serialize everything. So if you have 100 items to do and item 0 takes 200 seconds to complete, and items 1 - 99 take 1ms to complete, you will need to wait for task 0 to complete before you can start parsing the data. This will slow down the DWARF parser if you switch over to this. TaskRunner should not be deleted as it has a very specific purpose. Your TaskMap works fine for one case, but not in the other. > I did this change to help parallel symbol demangling (to come in a separate > patch). Rather than have the symbol demangler use batching, etc, I thought > it should be a higher level function. Make sure this is a win before switching demangling over to using threads. I tried to improve performance on demangling before and I got worse performance on MacOS when we tried it because all of the malloc contention and threading overhead. ================ Comment at: source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp:1988 //---------------------------------------------------------------------- - while (true) { - auto f = task_runner_extract.WaitForNextCompletedTask(); - if (!f.valid()) - break; - unsigned cu_idx; - bool clear; - std::tie(cu_idx, clear) = f.get(); - clear_cu_dies[cu_idx] = clear; - } + TaskMap(num_compile_units, 1, extract_fn); ---------------- This replacement is ok, since no expensive work is being done in the while loop that did the task_runner_extract.WaitForNextCompletedTask();. ================ Comment at: source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp:1994 - TaskRunner<uint32_t> task_runner; - for (uint32_t cu_idx = 0; cu_idx < num_compile_units; ++cu_idx) - task_runner.AddTask(parser_fn, cu_idx); - - while (true) { - std::future<uint32_t> f = task_runner.WaitForNextCompletedTask(); - if (!f.valid()) - break; - uint32_t cu_idx = f.get(); + TaskMap(num_compile_units, 1, parser_fn); ---------------- Note that we lost performance here. The old code would run: ``` while (true) { std::future<uint32_t> f = task_runner.WaitForNextCompletedTask(); // Do expensive work as soon as possible with any random task that completes as soon as it completes. ``` Your current code says "wait to do all expensive work until I complete everything and then do all of the expensive work". ================ Comment at: source/Utility/TaskPool.cpp:77 + +void TaskMap(size_t size, size_t batch, std::function<void(size_t)> const & func) +{ ---------------- Is this named correctly? Maybe SerializedTaskMap? Or BatchedTaskMap? ================ Comment at: source/Utility/TaskPool.cpp:100 + for (size_t i = 0; i < est_batches; i++) + futures[i].wait(); +} ---------------- TaskRunner is smart in the way it runs things: it lets you run N things and get each item as it completes. This implementation, if read it correctly, will serialize everything. So if you have 100 items to do and item at index 0 takes 200 seconds to complete, and items 1 - 99 take 1ms to complete, you will need to wait for task 0 to complete before you can start parsing the data. This will slow down the DWARF parser if you switch over to this. Repository: rL LLVM https://reviews.llvm.org/D32757 _______________________________________________ lldb-commits mailing list lldb-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
