linux-kernel - Re: checkpatch.pl is getting too slow

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Message-Id: <1233449877.5903.48.camel@desktop>
Date:	Sat, 31 Jan 2009 16:57:57 -0800
From:	Daniel Walker <dwalker@...o99.com>
To:	Andy Whitcroft <apw@...onical.com>
Cc:	Greg KH <greg@...ah.com>, linux-kernel@...r.kernel.org
Subject: Re: checkpatch.pl is getting too slow

On Sat, 2009-01-31 at 21:02 +0000, Andy Whitcroft wrote:
> On Sat, Jan 31, 2009 at 10:55:07AM -0800, Greg KH wrote:
> > Hi Andy,
> > 
> > I've noticed that checkpatch.pl is getting slower and slower when run on
> > a whole file, but yesterday I realized that it now is pretty much
> > unusable:
> > 
> > $ time ./scripts/checkpatch.pl --file drivers/staging/uc2322/aten2011.c
> > 
> > <snip>
> > total: 168 errors, 126 warnings, 3939 lines checked
> > 
> > drivers/staging/uc2322/aten2011.c has style problems, please review.  If any of these errors
> > are false positives report them to the maintainer, see
> > CHECKPATCH in MAINTAINERS.
> > 
> > real	8m7.924s
> > user	8m7.058s
> > sys	0m0.116s
> 
> That is scarey indeed.  Something is very wrong in there if it went back
> to a more reasonable 10's of seconds with a few patches.  I will have a
> look at the file you attached and see what I can find.
> 
> Thanks for the heads up.

After some debugging it looks like it takes a long time to processes
lines similar to,

/*************************************
 * Bit definitions for each register *
 *************************************/
#define LCR_BITS_5              0x00    /* 5 bits/char */
#define LCR_BITS_6              0x01    /* 6 bits/char */
#define LCR_BITS_7              0x02    /* 7 bits/char */
#define LCR_BITS_8              0x03    /* 8 bits/char */
#define LCR_BITS_MASK           0x03    /* Mask for bits/char field */


There's a section in the code which has several of these. The processing
slows down when this expression matches repeatedly,

# Check for potential 'bare' types
                my ($stat, $cond, $line_nr_next, $remain_next, $off_next);
                if ($realcnt && $line =~ /.\s*\S/) {
                        ($stat, $cond, $line_nr_next, $remain_next, $off_next) =
                                ctx_statement_block($linenr, $realcnt, 0);

and ctx_statement_block will process $realcnt lines trying to find a
complete block, and it has no concept of "define" so it just keep
processing until it's concept of a block ending.. That happens on each
"define" line in the file, which I think accounts for all the overhead.

I added the following temporary work around, which speeds things up
considerably. Just forcing it to only process one line at most.

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 45eb0ae..787423a 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -1357,7 +1357,7 @@ sub process {
 		my ($stat, $cond, $line_nr_next, $remain_next, $off_next);
 		if ($realcnt && $line =~ /.\s*\S/) {
 			($stat, $cond, $line_nr_next, $remain_next, $off_next) =
-				ctx_statement_block($linenr, $realcnt, 0);
+				ctx_statement_block($linenr, 1, 0);
 			$stat =~ s/\n./\n /g;
 			$cond =~ s/\n./\n /g;
 


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