What's the preferred way to post changes? In the past I tried emailing here but it was pointed out I should send to lldb-commit instead. But, there's also phabricator for web-based code reviews.
So, 1. just email lldb-commits? 2. post on http://reviews.llvm.org/? On Thu, Apr 20, 2017 at 3:16 AM, Pavel Labath <lab...@google.com> wrote: > Thank you very much for tracking this down. > > +1 for making UniqueCStringMap speak ConstString -- i think it just makes > sense given that it already has "unique" in the name. > > ConstString already has a GetStringRef accessor. Also adding a conversion > operator may be a good idea, although it probably won't help in all > situations (you'll still have to write StringRef(X).drop_front() etc. if > you want to do stringref operations on the string) > > pl > > On 20 April 2017 at 01:46, Zachary Turner <ztur...@google.com> wrote: > >> It doesn't entirely defeat the purpose, it's just not *as good* as making >> the interfaces take ConstStrings. StringRef already has a lot of safety >> and usability improvements over raw char pointers, and those improvements >> don't disappear just because you aren't using ConstString. Although I >> agree that if you can make it work where the interface only accepts and >> returns ConstStrings, and make conversion from ConstString to StringRef >> more seamless, that would be an even better improvement. >> >> On Wed, Apr 19, 2017 at 5:33 PM Scott Smith <scott.sm...@purestorage.com> >> wrote: >> >>> If I just assume the pointers are from ConstString, then doesn't that >>> defeat the purpose of making the interface safer? Why not use an actual >>> ConstString and provide conversion operators from ConstString to >>> StringRef? Seems we should be able to rely on the type system to get us >>> safety and performance. >>> >>> I'll try putting something together tomorrow. >>> >>> On Wed, Apr 19, 2017 at 4:48 PM, Zachary Turner <ztur...@google.com> >>> wrote: >>> >>>> The change was made to make the interface safer and allow propagation >>>> of StringRef through other layers. The previous code was already taking a >>>> const char *, and so it was working under the assumption that the const >>>> char* passed in came from a ConstString. As such, continuing to make that >>>> same assumption seems completely reasonable. >>>> >>>> So perhaps you can just change the operator to compare the pointers, as >>>> was being done before. >>>> >>>> On Wed, Apr 19, 2017 at 4:24 PM Scott Smith < >>>> scott.sm...@purestorage.com> wrote: >>>> >>>>> It looks like it was this change: >>>>> >>>>> commit 45fb8d00309586c3f7027f66f9f8a0b56bf1cc4a >>>>> Author: Zachary Turner <ztur...@google.com> >>>>> Date: Thu Oct 6 21:22:44 2016 +0000 >>>>> >>>>> Convert UniqueCStringMap to use StringRef. >>>>> >>>>> git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@283494 >>>>> 91177308-0d34-0410-b5e6-96231b3b80d8 >>>>> >>>>> >>>>> I'm guessing it's because the old code assumed const string, which >>>>> meant that uniqueness comparisons could be done by simply comparing the >>>>> pointer. Now it needs to use an actual string comparison routine. This >>>>> code: >>>>> >>>>> bool operator<(const Entry &rhs) const { return cstring < >>>>> rhs.cstring; } >>>>> >>>>> didn't actually change in the revision, but cstring went from 'const >>>>> char *' to 'StringRef'. If you know for sure that all the StringRefs come >>>>> from ConstString, then it'd be easy enough to change the comparison, but I >>>>> don't know how you guarantee that. >>>>> >>>>> I assume the change was made to allow proper memory cleanup when the >>>>> symbols are discarded? >>>>> >>>>> On Thu, Apr 13, 2017 at 5:37 AM, Pavel Labath <lab...@google.com> >>>>> wrote: >>>>> >>>>>> Bisecting the performance regression would be extremely valuable. If >>>>>> you want to do that, it would be very appreciated. >>>>>> >>>>>> On 12 April 2017 at 20:39, Scott Smith via lldb-dev < >>>>>> lldb-dev@lists.llvm.org> wrote: >>>>>> >>>>>>> For my app I think it's largely parsing debug symbols tables for >>>>>>> shared libraries. My main performance improvement was to increase the >>>>>>> parallelism of parsing that information. >>>>>>> >>>>>>> Funny, gdb/gold has a similar accelerator table (created when you >>>>>>> link with -gdb-index). I assume lldb doesn't know how to parse it. >>>>>>> >>>>>>> I'll work on bisecting the change. >>>>>>> >>>>>>> On Wed, Apr 12, 2017 at 12:26 PM, Jason Molenda <ja...@molenda.com> >>>>>>> wrote: >>>>>>> >>>>>>>> I don't know exactly when the 3.9 / 4.0 branches were cut, and what >>>>>>>> was done between those two points, but in general we don't expect/want >>>>>>>> to >>>>>>>> see performance regressions like that. I'm more familiar with the perf >>>>>>>> characteristics on macos, Linux is different in some important >>>>>>>> regards, so >>>>>>>> I can only speak in general terms here. >>>>>>>> >>>>>>>> In your example, you're measuring three things, assuming you have >>>>>>>> debug information for MY_PROGRAM. The first is "Do the initial read >>>>>>>> of the >>>>>>>> main binary and its debug information". The second is "Find all symbol >>>>>>>> names 'main'". The third is "Scan a newly loaded solib's symbols" >>>>>>>> (assuming you don't have debug information from solibs from /usr/lib >>>>>>>> etc). >>>>>>>> Technically there's some additional stuff here -- launching the >>>>>>>> process, >>>>>>>> detecting solibs as they're loaded, looking up the symbol context when >>>>>>>> we >>>>>>>> hit the breakpoint, backtracing a frame or two, etc, but that stuff is >>>>>>>> rarely where you'll see perf issues on a local debug session. >>>>>>>> >>>>>>>> Which of these is likely to be important will depend on your >>>>>>>> MY_PROGRAM. If you have a 'int main(){}', it's not going to be dwarf >>>>>>>> parsing. If your binary only pulls in three solib's by the time it is >>>>>>>> running, it's not going to be new module scanning. A popular place to >>>>>>>> spend >>>>>>>> startup time is in C++ name demangling if you have a lot of solibs >>>>>>>> with C++ >>>>>>>> symbols. >>>>>>>> >>>>>>>> >>>>>>>> On Darwin systems, we have a nonstandard accelerator table in our >>>>>>>> DWARF emitted by clang that lldb reads. The "apple_types", >>>>>>>> "apple_names" >>>>>>>> etc tables. So when we need to find a symbol named "main", for Modules >>>>>>>> that have a SymbolFile, we can look in the accelerator table. If that >>>>>>>> SymbolFile has a 'main', the accelerator table gives us a reference >>>>>>>> into >>>>>>>> the DWARF for the definition, and we can consume the DWARF lazily. We >>>>>>>> should never need to do a full scan over the DWARF, that's considered a >>>>>>>> failure. >>>>>>>> >>>>>>>> (in fact, I'm working on a branch of the llvm.org sources from >>>>>>>> mid-October and I suspect Darwin lldb is often consuming a LOT more >>>>>>>> dwarf >>>>>>>> than it should be when I'm debugging, I need to figure out what is >>>>>>>> causing >>>>>>>> that, it's a big problem.) >>>>>>>> >>>>>>>> >>>>>>>> In general, I've been wanting to add a new "perf counters" >>>>>>>> infrastructure & testsuite to lldb, but haven't had time. One thing I >>>>>>>> work >>>>>>>> on a lot is debugging over a bluetooth connection; it turns out that >>>>>>>> BT is >>>>>>>> very slow, and any extra packets we send between lldb and debugserver >>>>>>>> are >>>>>>>> very costly. The communication is so fast over a local host, or over >>>>>>>> a usb >>>>>>>> cable, that it's easy for regressions to sneak in without anyone >>>>>>>> noticing. >>>>>>>> So the original idea was hey, we can have something that counts >>>>>>>> packets for >>>>>>>> distinct operations. Like, this "next" command should take no more >>>>>>>> than 40 >>>>>>>> packets, that kind of thing. And it could be expanded -- "b main >>>>>>>> should >>>>>>>> fully parse the DWARF for only 1 symbol", or "p *this should only look >>>>>>>> up 5 >>>>>>>> types", etc. >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> > On Apr 12, 2017, at 11:26 AM, Scott Smith via lldb-dev < >>>>>>>> lldb-dev@lists.llvm.org> wrote: >>>>>>>> > >>>>>>>> > I worked on some performance improvements for lldb 3.9, and was >>>>>>>> about to forward port them so I can submit them for inclusion, but I >>>>>>>> realized there has been a major performance drop from 3.9 to 4.0. I am >>>>>>>> using the official builds on an Ubuntu 16.04 machine with 16 cores / 32 >>>>>>>> hyperthreads. >>>>>>>> > >>>>>>>> > Running: time lldb-4.0 -b -o 'b main' -o 'run' MY_PROGRAM > >>>>>>>> /dev/null >>>>>>>> > >>>>>>>> > With 3.9, I get: >>>>>>>> > real 0m31.782s >>>>>>>> > user 0m50.024s >>>>>>>> > sys 0m4.348s >>>>>>>> > >>>>>>>> > With 4.0, I get: >>>>>>>> > real 0m51.652s >>>>>>>> > user 1m19.780s >>>>>>>> > sys 0m10.388s >>>>>>>> > >>>>>>>> > (with my changes + 3.9, I got real down to 4.8 seconds! But I'm >>>>>>>> not convinced you'll like all the changes.) >>>>>>>> > >>>>>>>> > Is this expected? I get roughly the same results when compiling >>>>>>>> llvm+lldb from source. >>>>>>>> > >>>>>>>> > I guess I can spend some time trying to bisect what happened. >>>>>>>> 5.0 looks to be another 8% slower. >>>>>>>> > >>>>>>>> > _______________________________________________ >>>>>>>> > lldb-dev mailing list >>>>>>>> > lldb-dev@lists.llvm.org >>>>>>>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev >>>>>>>> >>>>>>>> >>>>>>> >>>>>>> _______________________________________________ >>>>>>> lldb-dev mailing list >>>>>>> lldb-dev@lists.llvm.org >>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev >>>>>>> >>>>>>> >>>>>> >>>>> >>> >
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