From: Alan Mackenzie <acm@muc.de>
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: 16526-done@debbugs.gnu.org
Subject: bug#16526: 24.3.50; scroll-conservatively & c-mode regression
Date: Sat, 28 Jun 2014 13:00:59 +0000 [thread overview]
Message-ID: <20140628130059.GA4144@acm.acm> (raw)
In-Reply-To: <jwv8uoim0bm.fsf-monnier+emacsbugs@gnu.org>
Hi, Stefan.
On Fri, Jun 27, 2014 at 06:54:55PM -0400, Stefan Monnier wrote:
> >> Could scan-lists be exhausting some sort of resource in this particular
> >> invocation which needs ~0.7s to replenish? Or something like that?
> > Or a GC call or something like that? Can't think of any reason why that
> > could happen, no.
> One way to figure it out is to change your code such that scan-lists is
> always called twice in a row. If the time spend is the same both time,
> then it's definitely not some sort of resources exhaustion that just
> happens to slow down this one particular call.
Yes, the second call takes as long as the first call.
One thing that did make a big difference was binding
parse-sexp-ignore-comments to nil around a call to scan-lists. My two
calls to (scan-lists 947171 -1 1) give these results:
parse-sexp-ignore-comments | end position time
---------------------------------------------------------------------
t | 919215 0.6976802349090576
nil | 899080 0.0021085739135742188
So, although with parse-..-comments nil, the distance traversed was
greater, the time taken was a factor ~300 less. This suggests that
comments have something to do with the problem.
parse_sexp_ignore_comments is only tested twice in scan_lists. The first
time, it is only setting up syntax table variables and suchlike after
having half-detected a comment closer. The second time, back_comment
gets called. It seems likely the problem is in back_comment.
AH!!!!! GOT IT!!!! What causes the slowdown is binding
open-paren-in-column-0-is-defun-start to nil around the scan-lists. In
CC Mode's "engine" parts, that variable is bound to nil. There are good
reasons for this (which I can't precisely recall just at the moment).
In CC Mode, "'" has string syntax. So any C comment with an odd number
of apostrophes looks, to back_comment, like it has an "unbalanced string",
and the code ends up at label lossage: in back_comment. Here
find_defun_start is called, and this returns BOB when open-paren-..-0 is
nil. From here (BOB) the code scans forward to check this putative
"unbalanced string". It's a long way from BOB to ~900k, hence the
sluggishness.
Where do we go from here?
> Stefan
--
Alan Mackenzie (Nuremberg, Germany).
next prev parent reply other threads:[~2014-06-28 13:00 UTC|newest]
Thread overview: 93+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <mailman.12613.1390467262.10748.bug-gnu-emacs@gnu.org>
2014-01-23 8:53 ` bug#16526: 24.3.50; scroll-conservatively & c-mode regression martin rudalics
2014-01-24 15:45 ` martin rudalics
2014-01-24 20:48 ` Alan Mackenzie
[not found] ` <lbujij$1scv$1@colin.muc.de>
2014-01-25 3:50 ` Juanma Barranquero
2014-01-25 9:23 ` martin rudalics
[not found] ` <52E38286.1050306@gmx.at>
2014-01-25 10:30 ` Eli Zaretskii
2014-01-25 14:58 ` martin rudalics
[not found] ` <52E3D131.2090705@gmx.at>
2014-01-25 16:30 ` Eli Zaretskii
2014-01-25 16:48 ` martin rudalics
2014-01-25 17:29 ` Eli Zaretskii
2014-01-25 18:25 ` martin rudalics
[not found] ` <52E4019C.5080905@gmx.at>
2014-01-25 18:31 ` Eli Zaretskii
2014-01-25 18:40 ` Eli Zaretskii
2014-01-26 11:20 ` martin rudalics
[not found] ` <52E4EF61.3050404@gmx.at>
2014-01-26 17:20 ` Eli Zaretskii
2014-01-26 20:43 ` Alan Mackenzie
2014-01-27 8:21 ` martin rudalics
2014-01-29 21:52 ` Alan Mackenzie
2014-01-30 17:16 ` Eli Zaretskii
2014-01-31 20:00 ` Alan Mackenzie
2014-01-31 20:16 ` Eli Zaretskii
[not found] ` <52E61704.6050807@gmx.at>
2014-01-27 14:49 ` Stefan Monnier
[not found] ` <jwvvbx5fq2b.fsf-monnier+emacsbugs@gnu.org>
2014-01-27 17:25 ` martin rudalics
[not found] ` <52E69695.5040703@gmx.at>
2014-01-28 0:16 ` Stefan Monnier
2014-01-29 22:36 ` Alan Mackenzie
[not found] ` <20140129223626.GD3092@acm.acm>
2014-01-30 7:37 ` martin rudalics
2014-01-30 13:47 ` martin rudalics
[not found] ` <52EA57D6.5080403@gmx.at>
2014-01-30 17:15 ` Eli Zaretskii
2014-01-30 18:58 ` martin rudalics
[not found] ` <52EAA0C9.1090000@gmx.at>
2014-02-01 10:41 ` Eli Zaretskii
2014-02-02 13:18 ` martin rudalics
2014-02-02 17:40 ` Alan Mackenzie
[not found] ` <20140202174050.GA5365@acm.acm>
2014-02-02 18:07 ` Eli Zaretskii
2014-02-02 19:20 ` Alan Mackenzie
2014-02-02 20:53 ` Eli Zaretskii
2014-02-05 23:00 ` Alan Mackenzie
2014-02-06 6:01 ` Eli Zaretskii
2014-06-22 16:49 ` Eli Zaretskii
2014-06-22 19:32 ` Alan Mackenzie
2014-06-22 20:04 ` Eli Zaretskii
2014-06-25 21:32 ` Alan Mackenzie
2014-06-26 2:51 ` Stefan Monnier
2014-06-27 20:34 ` Alan Mackenzie
2014-06-27 22:33 ` Stefan Monnier
2014-06-27 22:54 ` Stefan Monnier
[not found] ` <jwv8uoim0bm.fsf-monnier+emacsbugs@gnu.org>
2014-06-28 13:00 ` Alan Mackenzie [this message]
2014-06-28 14:00 ` martin rudalics
2014-06-28 14:34 ` Stefan Monnier
[not found] ` <53AECA88.7010401@gmx.at>
2014-06-28 14:55 ` Alan Mackenzie
2014-06-28 15:12 ` Eli Zaretskii
2014-06-28 16:30 ` Alan Mackenzie
2014-06-29 8:44 ` martin rudalics
2014-06-29 9:17 ` Alan Mackenzie
2014-06-29 10:06 ` martin rudalics
[not found] ` <53AFE536.7010407@gmx.at>
2014-06-29 12:48 ` Alan Mackenzie
2014-06-29 14:18 ` martin rudalics
2014-06-29 14:41 ` Alan Mackenzie
[not found] ` <20140629144151.GD2948@acm.acm>
2014-06-29 16:01 ` martin rudalics
[not found] ` <53B03876.9070307@gmx.at>
2014-06-29 17:49 ` Alan Mackenzie
2014-06-30 7:55 ` martin rudalics
2014-06-30 13:48 ` Stefan Monnier
[not found] ` <53B117D6.1050306@gmx.at>
2014-07-02 20:05 ` Alan Mackenzie
[not found] ` <20140702200522.GB3823@acm.acm>
2014-07-03 1:57 ` Stefan Monnier
2014-07-03 8:40 ` martin rudalics
[not found] ` <jwv61jf2owy.fsf-monnier+emacsbugs@gnu.org>
2014-07-03 14:59 ` Stefan Monnier
2014-07-04 18:27 ` Alan Mackenzie
2014-07-04 19:11 ` Stefan Monnier
2014-07-04 19:43 ` Stefan Monnier
2014-07-05 2:23 ` Stefan Monnier
2014-07-06 13:48 ` Alan Mackenzie
2014-07-07 1:52 ` Stefan Monnier
2014-07-07 7:07 ` martin rudalics
[not found] ` <jwvsimevsvz.fsf-monnier+emacsbugs@gnu.org>
2014-07-07 7:07 ` martin rudalics
2014-07-05 20:25 ` Alan Mackenzie
2014-07-05 23:06 ` Stefan Monnier
2014-07-04 19:29 ` Alan Mackenzie
2014-07-05 1:52 ` Stefan Monnier
2014-07-05 7:47 ` Alan Mackenzie
2014-06-29 22:14 ` Stefan Monnier
[not found] ` <jwvionjjrn7.fsf-monnier+emacsbugs@gnu.org>
2014-07-02 18:40 ` Alan Mackenzie
[not found] ` <20140702184013.GA3823@acm.acm>
2014-07-02 19:40 ` Stefan Monnier
[not found] ` <jwvsimpksv1.fsf-monnier+emacsbugs@gnu.org>
2014-06-28 17:33 ` Alan Mackenzie
[not found] ` <20140628173334.GB2632@acm.acm>
2014-06-29 21:39 ` Stefan Monnier
2014-01-27 8:20 ` martin rudalics
2014-01-27 16:23 ` Eli Zaretskii
2014-01-27 17:26 ` martin rudalics
2014-01-26 11:19 ` martin rudalics
2014-01-25 20:27 ` bug#16526: 24.3.50; scroll-conservatively & c-mode regression. The purpose of revision 116070 Alan Mackenzie
[not found] ` <20140125202721.GA3630@acm.acm>
2014-01-25 23:02 ` Stefan Monnier
2014-01-26 3:41 ` Eli Zaretskii
2014-01-26 9:54 ` Alan Mackenzie
2014-01-26 16:33 ` Eli Zaretskii
2014-01-26 17:35 ` Eli Zaretskii
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