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Date: Mon, 15 Feb 2021 16:21:14 +0100
From: Jan Hubicka <hubicka@ucw.cz>
To: "marxin at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
Cc: gcc-bugs@gcc.gnu.org
Subject: Re: [Bug gcov-profile/99105] profile streaming scales poorly to
 projects with many source files
Message-ID: <20210215152114.GH44975@kam.mff.cuni.cz>
References: <bug-99105-4@http.gcc.gnu.org/bugzilla/>
 <bug-99105-4-vNRCjU2v31@http.gcc.gnu.org/bugzilla/>
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> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99105
> 
> --- Comment #8 from Martin Liška <marxin at gcc dot gnu.org> ---
> This is what I see for GCC PGO in train stage. It's from perf top:
> 
>    4.33%  cc1plus                          [.] __gcov_indirect_call_profiler_v4
>                                  ◆
>    2.28%  cc1plus                          [.] __gcov_topn_values_profiler     
>                                  ▒
>    0.85%  cc1plus                          [.] ggc_internal_alloc              

Yep, this is usual profile I see.  Perhaps you want to try profile "make check"
> 
> In the case of GCC, we emit 500 .gcda files.
> 
> @Honza: Can you please test my patch that uses glibc buffered I/O if it helps?

I can give it a try later this week (I would like to collect some data on performance first)

Honza