[coldfire-gnu-discuss] NPTL on 547x cpus

[Maxim Kuvyrkov]

On 5/14/10 5:30 PM, Wong, Ken wrote:
...
> Aside from the unexplained jump in processor usage, our ~2 week
> evaluation didn't uncover any bugs with the 4.4 toolchain related to
> NPTL.

I have a guess about the jump in processor usage on thread-heavy 
applications.

Thread-local storage (TLS) and NPTL on ColdFire requires kernel support, 
e.g., to implement atomic compare-and-exchange operation.  This support 
can be delivered to applications and libraries via kernel system calls 
or via kernel vDSO.  The main difference between system calls and calls 
to vDSO is that the latter does not involve context switching, so it is 
substantially faster.  From user-space perspective, kernel vDSO acts 
just like a shared library.

Unfortunately, vDSO support for ColdFire kernel was not finished, so 
current ColdFire kernels do not provide it.  Hence the libpthread and 
other EGLIBC libraries fallback to system call interface to get required 
functionality.

-- 
Maxim Kuvyrkov
CodeSourcery
maxim at codesourcery.com
(650) 331-3385 x724