From: Bill Wendling <morbo@google.com>
To: dwarves@vger.kernel.org, bpf <bpf@vger.kernel.org>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Subject: Re: [RFC 0/1] Combining CUs into a single hash table
Date: Tue, 23 Feb 2021 12:44:58 -0800 [thread overview]
Message-ID: <CAGG=3QWuxzwKGuYhVu+EfXPFZMNsO7-=NtHbdXAyvcVjvKF3hA@mail.gmail.com> (raw)
In-Reply-To: <20210212211607.2890660-1-morbo@google.com>
Bump for exposure.
On Fri, Feb 12, 2021 at 1:16 PM Bill Wendling <morbo@google.com> wrote:
>
> Hey gang,
>
> I would like your feedback on this patch.
>
> This patch creates one hash table that all CUs share. The impetus for this
> patch is to support clang's LTO (Link-Time Optimizations). Currently, pahole
> can't handle the DWARF data that clang produces, because the CUs may refer to
> tags in other CUs (all of the code having been squozen together).
>
> One solution I found is to process the CUs in two steps:
>
> 1. add the CUs into a single hash table, and
> 2. perform the recoding and finalization steps in a a separate step.
>
> The issue I'm facing with this patch is that it balloons the runtime from
> ~11.11s to ~14.27s. It looks like the underlying cause is that some (but not
> all) hash buckets have thousands of entries each. I've bumped up the
> HASHTAGS__BITS from 15 to 16, which helped a little. Bumping it up to 17 or
> above causes a failure.
>
> A couple of things I thought of may help. We could increase the number of
> buckets, which would help with distribution. As I mentioned though, that seemed
> to cause a failure. Another option is to store the bucket entries in a
> non-list, e.g. binary search tree.
>
> I wanted to get your opinions before I trod down one of these roads.
>
> Share and enjoy!
> -bw
>
> Bill Wendling (1):
> dwarf_loader: have all CUs use a single hash table
>
> dwarf_loader.c | 45 +++++++++++++++++++++++++++++++++------------
> 1 file changed, 33 insertions(+), 12 deletions(-)
>
> --
> 2.30.0.478.g8a0d178c01-goog
>
next prev parent reply other threads:[~2021-02-23 20:47 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-12 21:16 [RFC 0/1] Combining CUs into a single hash table Bill Wendling
2021-02-12 21:16 ` [RFC PATCH 1/1] dwarf_loader: have all CUs use " Bill Wendling
2021-02-23 20:44 ` Bill Wendling [this message]
2021-02-23 20:54 ` [RFC 0/1] Combining CUs into " Arnaldo Carvalho de Melo
2021-03-14 7:05 ` Yonghong Song
2021-03-14 8:28 ` Bill Wendling
2021-03-14 23:33 ` Yonghong Song
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