On 16 January 2018 at 18:19, Dave Watson <davejwat...@fb.com> wrote: > On 01/16/18 09:34 AM, Luke Diamand wrote: >> On 16 January 2018 at 03:33, Luke Diamand <l...@diamand.org> wrote: >> > Hi! >> > >> > 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: >> > >> > https://gist.github.com/luked99/7c67d94da5c33cac5a1b41a500013355 > > I think there is a similar perf test program under tests/, 'make perf' > >> > >> > 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? >> >> If do: >> export UNW_ARM_UNWIND_METHOD=4 >> >> (so only use the exidx tables) then it drops from ~1ms to 95us. >> >> My image only has the exidx tables; it's built with gcc using >> bog-standard compiler and linker options. >> >> $ objdump -S bt_perf >> Idx Name Size VMA LMA File off Algn >> .... >> 15 .ARM.extab 00000264 0000a7e8 0000a7e8 0000a7e8 2**2 >> CONTENTS, ALLOC, LOAD, READONLY, DATA >> 16 .ARM.exidx 000002a0 0000aa4c 0000aa4c 0000aa4c 2**2 >> CONTENTS, ALLOC, LOAD, READONLY, DATA >> 17 .eh_frame 00000004 0000acec 0000acec 0000acec 2**2 >> CONTENTS, ALLOC, LOAD, READONLY, DATA > > I didn't notice anything in particular looking at the commit logs. > I'll try and repro when I get a chance
arm_find_proc_info() seems to start out trying eh_frame tables. Isn't it always best on ARM to start looking in the exidx tables? _______________________________________________ Libunwind-devel mailing list Libunwind-devel@nongnu.org https://lists.nongnu.org/mailman/listinfo/libunwind-devel
