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[Libunwind-devel] unw_backtrace(): Performance slowdown for ARM?

From: Luke Diamand
Subject: [Libunwind-devel] unw_backtrace(): Performance slowdown for ARM?
Date: Tue, 16 Jan 2018 03:33:12 +0000


I could be wrong about this, but I'm finding a roughly 10x slowdown on
ARM between 1.2.1 and current HEAD (e1ca8748).

I have a small test program here:

On my Raspberry Pi 2, this is getting ~180us to do a self-backtrace in
1.2.1 and around 1.8ms in HEAD.

I tried running perf, and that seems to be saying that it is opening
and closing files a lot.

I also had a go at git bisecting, but there's a separate bug which was
introduced and then fixed which caused it to segfault, which overlaps
with this problem, along with some other performance regression fixes.

90d0d15c4ec3bb812dcb44c081757ebf6756cc6b didn't crash, but was slow.
2a5d1a629634b3225fccb1ed8a0a765bccc77f2e crashed.
v1.2.1 is fast.

I'm configuring with:

CC=arm-linux-gnueabihf-gcc CFLAGS="-g" configure --disable-debug
--host=arm-linux \
    --enable-shared --disable-static --with-sysroot=/home/lgd/arm
--enable-maintainer-mode \
    --disable-debug-frame --disable-block-signals

Any ideas as to what's going on?


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