Messages in this thread | | | Date | Sun, 1 Sep 2019 19:24:03 +0200 | From | Pavel Machek <> | Subject | Re: [PATCH] scripts: coccinelle: check for !(un)?likely usage |
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Hi!
> > This patch adds coccinelle script for detecting !likely and !unlikely > > usage. It's better to use unlikely instead of !likely and vice versa. > > Please explain _why_ is it better in the changelog. > > btw: there are relatively few uses like this in the kernel. > > $ git grep -P '!\s*(?:un)?likely\s*\(' | wc -l > 40 > > afaict: It may save 2 bytes of x86/64 object code. > > For instance: > > $ diff -urN kernel/tsacct.lst.old kernel/tsacct.lst.new|less > --- kernel/tsacct.lst.old 2019-08-25 09:21:39.936570183 -0700 > +++ kernel/tsacct.lst.new 2019-08-25 09:22:20.774324886 -0700 > @@ -24,158 +24,153 @@ > 15: 48 89 fb mov %rdi,%rbx > u64 time, delta; > > - if (!likely(tsk->mm)) > + if (unlikely(tsk->mm))
Are you sure this is equivalent?
Pavel
> 18: 4c 8d ab 28 02 00 00 lea 0x228(%rbx),%r13 > 1f: e8 00 00 00 00 callq 24 <__acct_update_integrals+0x24> > 20: R_X86_64_PLT32 __sanitizer_cov_trace_pc-0x4 > 24: 4c 89 ef mov %r13,%rdi > 27: e8 00 00 00 00 callq 2c <__acct_update_integrals+0x2c> > 28: R_X86_64_PLT32 __asan_load8_noabort-0x4 > - 2c: 4c 8b bb 28 02 00 00 mov 0x228(%rbx),%r15 > - 33: 4d 85 ff test %r15,%r15 > - 36: 74 34 je 6c <__acct_update_integrals+0x6c> > + 2c: 48 83 bb 28 02 00 00 cmpq $0x0,0x228(%rbx) > + 33: 00 > + 34: 75 34 jne 6a <__acct_update_integrals+0x6a> > return; > > And here's a possible equivalent checkpatch test. > --- > scripts/checkpatch.pl | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl > index 287fe73688f0..364603ad1a47 100755 > --- a/scripts/checkpatch.pl > +++ b/scripts/checkpatch.pl > @@ -6529,6 +6529,24 @@ sub process { > "Using $1 should generally have parentheses around the comparison\n" . $herecurr); > } > > +# !(likely|unlikely)(condition) use should be (unlikely|likely)(condition) > + if ($perl_version_ok && > + $line =~ /(\!\s*((?:un)?likely))\s*$balanced_parens/) { > + my $match = $1; > + my $type = $2; > + my $reverse; > + if ($type eq "likely") { > + $reverse = "unlikely"; > + } else { > + $reverse = "likely"; > + } > + if (WARN("LIKELY_MISUSE", > + "Prefer $reverse over $match\n" . $herecurr) && > + $fix) { > + $fixed[$fixlinenr] =~ s/\Q$match\E\s*\(/$reverse(/; > + } > + } > + > # whine mightly about in_atomic > if ($line =~ /\bin_atomic\s*\(/) { > if ($realfile =~ m@^drivers/@) { >
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