netdev - Re: [RFC bpf-next 07/16] kallsyms: Use rb tree for kallsyms name search

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Message-ID: <20201028211502.ishg56ogvjuj7t4w@ast-mbp.dhcp.thefacebook.com>
Date:   Wed, 28 Oct 2020 14:15:02 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>, Daniel Xu <dxu@...uu.xyz>,
        Steven Rostedt <rostedt@...dmis.org>,
        Jesper Brouer <jbrouer@...hat.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Viktor Malik <vmalik@...hat.com>
Subject: Re: [RFC bpf-next 07/16] kallsyms: Use rb tree for kallsyms name
 search

On Wed, Oct 28, 2020 at 07:25:34PM +0100, Jiri Olsa wrote:
> On Thu, Oct 22, 2020 at 10:21:29AM +0200, Jiri Olsa wrote:
> > The kallsyms_expand_symbol function showed in several bpf related
> > profiles, because it's doing linear search.
> > 
> > Before:
> > 
> >  Performance counter stats for './src/bpftrace -ve kfunc:__x64_sys_s* \
> >    { printf("test\n"); } i:ms:10 { printf("exit\n"); exit();}' (5 runs):
> > 
> >      2,535,458,767      cycles:k                         ( +-  0.55% )
> >        940,046,382      cycles:u                         ( +-  0.27% )
> > 
> >              33.60 +- 3.27 seconds time elapsed  ( +-  9.73% )
> > 
> > Loading all the vmlinux symbols in rbtree and and switch to rbtree
> > search in kallsyms_lookup_name function to save few cycles and time.
> > 
> > After:
> > 
> >  Performance counter stats for './src/bpftrace -ve kfunc:__x64_sys_s* \
> >    { printf("test\n"); } i:ms:10 { printf("exit\n"); exit();}' (5 runs):
> > 
> >      2,199,433,771      cycles:k                         ( +-  0.55% )
> >        936,105,469      cycles:u                         ( +-  0.37% )
> > 
> >              26.48 +- 3.57 seconds time elapsed  ( +- 13.49% )
> > 
> > Each symbol takes 160 bytes, so for my .config I've got about 18 MBs
> > used for 115285 symbols.
> > 
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> 
> FYI there's init_kprobes dependency on kallsyms_lookup_name in early
> init call, so this won't work as it is :-\ will address this in v2
> 
> also I'll switch to sorted array and bsearch, because kallsyms is not
> dynamically updated

wait wat? kallsyms are dynamically updated. bpf adds and removes from it.
You even worked on some of those patches :)