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From: Nick Desaulniers <ndesaulniers@google.com>
To: Linus Torvalds <torvalds@linux-foundation.org>,
	Masahiro Yamada <masahiroy@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: Very slow clang kernel config ..
Date: Fri, 30 Apr 2021 17:40:56 -0700	[thread overview]
Message-ID: <CAKwvOd=56=XJ9UPKVYJ=pTRGMNzdQe5k-rsx=66XQhWtrwtEqQ@mail.gmail.com> (raw)
In-Reply-To: <CAKwvOdkp_P8BCtFuKqDrtC_=A89ZfDf66Yr3FL2e=ojwv4KaMA@mail.gmail.com>

On Fri, Apr 30, 2021 at 5:25 PM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Fri, Apr 30, 2021 at 5:23 PM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > On Fri, Apr 30, 2021 at 5:19 PM Nick Desaulniers
> > <ndesaulniers@google.com> wrote:
> > >
> > > A quick:
> > > $ perf record -e cycles:pp --call-graph lbr make LLVM=1 LLVM_IAS=1
> > > -j72 allmodconfig
> > > $ perf report --no-children --sort=dso,symbol
> > > shows:
> > >      2.35%  [unknown]                [k] 0xffffffffabc00fc7
> > > +    2.29%  libc-2.31.so             [.] _int_malloc
> > >      1.24%  libc-2.31.so             [.] _int_free
> > > +    1.23%  ld-2.31.so               [.] do_lookup_x
> >
> > ^ bfd
>
>
> > > +    0.63%  ld-2.31.so               [.] _dl_lookup_symbol_x
> >
> > ^ bfd
>
> Ah, no, sorry, these are the runtime link editor/loader. So probably
> spending quite some time resolving symbols in large binaries.

I don't see NOW in:
$ llvm-readelf -Wd `which clang`
so I don't think clang was linked as `-Wl,-z,now`. I also see both
.hash and .gnu.hash in
$ llvm-readelf -S `which clang`.

The presence of NOW or lack of .gnu.hash would have been my guess for
symbol lookup issues. Perhaps the length of C++ mangled symbols
doesn't help.
-- 
Thanks,
~Nick Desaulniers

  reply	other threads:[~2021-05-01  0:41 UTC|newest]

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-29 21:53 Very slow clang kernel config Linus Torvalds
2021-04-30  0:19 ` Nick Desaulniers
2021-04-30  2:22   ` Nick Desaulniers
2021-05-01  0:19     ` Nick Desaulniers
2021-05-01  0:23       ` Nick Desaulniers
2021-05-01  0:25         ` Nick Desaulniers
2021-05-01  0:40           ` Nick Desaulniers [this message]
2021-05-01  1:22           ` Linus Torvalds
2021-05-01  1:48             ` Nick Desaulniers
2021-05-01  2:16               ` Fangrui Song
2021-05-01  3:32               ` Tom Stellard
2021-05-01 16:32                 ` Linus Torvalds
2021-05-01 19:57                   ` Serge Guelton
2021-05-01 22:39                     ` Linus Torvalds
2021-05-01 23:55                       ` Fangrui Song
2021-05-01 21:58                   ` David Laight
2021-05-02  9:31                   ` Adrian Bunk
2021-05-02 11:35                     ` David Laight
2021-05-02 16:12                     ` Linus Torvalds
2021-05-02 16:45                       ` Adrian Bunk
2021-05-02 16:49                         ` Linus Torvalds
2021-05-02 17:55                           ` Adrian Bunk
2021-05-02 17:59                             ` Linus Torvalds
2021-05-02 21:48                               ` Adrian Bunk
2021-05-04 22:02                                 ` Miguel Ojeda
2021-05-05  0:58                                   ` Theodore Ts'o
2021-05-05 17:21                                     ` Miguel Ojeda
2021-05-04 21:32                     ` Miguel Ojeda
2021-05-05 11:05                       ` David Laight
2021-05-05 13:53                         ` Miguel Ojeda
2021-05-05 14:13                           ` David Laight
2021-05-05 16:06                             ` Miguel Ojeda
2021-05-05 16:25                               ` David Laight
2021-05-05 17:55                                 ` Miguel Ojeda
2021-05-03  1:03                   ` Maciej W. Rozycki
2021-05-03 14:38                     ` Theodore Ts'o
2021-05-03 14:54                       ` Theodore Ts'o
2021-05-03 17:14                         ` Maciej W. Rozycki
2021-05-03 16:09                       ` David Laight
2021-05-04 23:04                       ` Greg Stark
2021-05-05  0:55                         ` Theodore Ts'o
2021-05-01 23:37               ` Mike Hommey
2021-05-02  5:19               ` Dan Aloni
2021-05-03 16:48                 ` Tom Stellard
2021-05-03 19:00                   ` Fangrui Song
2021-04-30  0:52 ` Nathan Chancellor
2021-04-30  2:21   ` Nick Desaulniers

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