[Fontconfig] libfontconfig.so.1.8.0's performance is not good on Ubuntu (version 2.11.0)

[Guangmu Zhu]

Hi,

It confused me very often when I was using Chrome that libfontconfig.so
occupied too much CPU resources only when Chrome was loading a page with
Chinese fonts such as SimSun and Microsoft YaHei. It haven't happened
with English fonts. Actually, the .so was always the top or second in
`perf top`.
I have read some source codes and downloaded the debug pkg. In .so's
DSO, a function not in symbol table usually took 90+% resources. The
address was located between 0x1e190-0x1e360. According to debug pkg's
symbol table and disassembled codes with objdump, all of these are a
series of FcStrCaseWalker* functions and Ucs-Utf transcoding functions.
And the function FcStrCaseWalkerNext's address(0x1e190) would appear
usually.
I read some source codes about FcStrCaseWalkerNext and its caller, but
they seem harmless. And I tried some sample programs and a program I
wrote, all worked very well. I guess, perhaps the function was called
very often when using FcConfig*, FcPattern*, FcFontSet* to GetObject or
GetString.
On my computer(Thinkpad X240s i7-4500u), the problem could make devices'
temperatures rise rapidly from 113 ℉ to 149 ℉ and cool down slowly for
the .so would occupy much CPU resources always. Maybe someone could tell
me how to deal with it?

Thanks in advance.