Yes (still guessing), the discard events are likely to be a major part of the cost.
But don't take my guesses too seriously -- measurement may show something different. On Tue, Nov 21, 2017 at 6:27 AM, Michael Dorman <mdor...@nvidia.com> wrote: > Hey, Jeffrey, > > > > So just to confirm, generating an event (thus requiring processing and > $recce->resume()) is part of this cost, yes? > > > > Michael Dorman > > > > *From:* marpa-parser@googlegroups.com [mailto:marpa-parser@ > googlegroups.com] *On Behalf Of *Jeffrey Kegler > *Sent:* Monday, November 20, 2017 5:09 PM > *To:* Marpa Parser Mailing LIst <marpa-parser@googlegroups.com> > *Subject:* Re: Are there good strategies for diagnosing performance > issues? > > > > I'm very rusty at looking at profiles of Marpa::R2, but I hope some > off-the-top-of-my-head remarks might be useful. Typically, almost all the > time of an R2 parse is taken up by the Perl layer, and by the semantics -- > the parse itself is almost free. So looking at how you handle the > semantics may help. In particular, the fewer Perl callbacks you use, the > faster you are likely to run. > > > > Marpa::R3, when it's fully developed, will allow more of the semantics to > be done inside Marpa itself, without callbacks, and should be faster. > > > > On Mon, Nov 20, 2017 at 1:52 PM, <mdor...@nvidia.com> wrote: > > Hey, all, > > > > I’ve been hoping for some time to replace an existing parser---implemented > using YAPP and a custom lexer---with a parser implemented using Marpa::R2. > > > > After a moderate amount of work, I finally got a working parser. > > > > The grammar is far easier to understand and work with than the old YAPP > parser; because we’re dealing with an indentation based format, I do have > to use a discard event to track indentation depths and emit indentation > tokens and the like. > > > > However, it’s disappointingly slow, taking about twice as long to parse > our full set of files. That was *really* unexpected. > > > > Immediately suspecting my code, I cranked my pathological case through > Devel::NYTProf; imagine my surprise when the top entry in the list of ‘top > 15 subroutines’ was an xsub: Marpa::R2::Thin::V::stack_step > <https://groups.google.com/forum/parser-1-line.html#Marpa__R2__Thin__V__stack_step>. > And this wasn’t by a small amount: that routine took 556s out of 590s or > so, and the next most expensive routine is Marpa::R2::Thin::SLR::read at > 12.7s. These completely dominated the total runtime. > > > > While I will try to sanitize my parser and make it postable so people can > perhaps point out problems, I thought I might first just ask: is that sort > of high cost in stack_step generally representative of some sort of problem > in the grammar? Is there some well-known construct that leads to a blow-up > that is easily eliminated, etc.? Is there something I could log or examine > that might shed some light? > > > > Any guidance would be appreciated. > > > > Michael Dorman > > -- > You received this message because you are subscribed to the Google Groups > "marpa parser" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to marpa-parser+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > > > > -- > You received this message because you are subscribed to the Google Groups > "marpa parser" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to marpa-parser+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > ------------------------------ > This email message is for the sole use of the intended recipient(s) and > may contain confidential information. Any unauthorized review, use, > disclosure or distribution is prohibited. If you are not the intended > recipient, please contact the sender by reply email and destroy all copies > of the original message. > ------------------------------ > > -- > You received this message because you are subscribed to the Google Groups > "marpa parser" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to marpa-parser+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "marpa parser" group. To unsubscribe from this group and stop receiving emails from it, send an email to marpa-parser+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
