Re: cpuset/affinity interfaces and TSX lock elision in musl

[Rich Felker <dalias@aerifal.cx>]

On Thu, May 16, 2013 at 06:37:01PM +0200, Daniel Cegiełka wrote:
> 1) Are there any plans to add support for cpuset/affinity interfaces?

I sat down to do it one day, and it was so ugly I got sick and put it
off again. Seriously. There's a huge abundance of CPU_*
macros/functions for manipulating abstract bitsets, but all "cpu set"
specific for no good reason.

If anyone wants to volunteer to do these, it would be a big relief to
me. Some caveats:

1. The glibc versions invoke UB by accessing past the end of the
__bits array in the macros that work with arbitrary-size sets. A
correct version would just cast the input pointer to a pointer to
unsigned long.

2. The glibc version has buggy overflow checks that were just fixed in
their git (so don't coppy the buggy logic).

3. These macros are sufficiently complex that they probably quality as
actual-code (with copyrightable content) in header files, and I don't
like that. Maybe we should make the external functions instead?

Discussion of these points and other ideas for implementing them is
welcome.

> 2) The upcoming glibc will have support for TSX lock elision.
> 
> http://en.wikipedia.org/wiki/Transactional_Synchronization_Extensions
> 
> http://lwn.net/Articles/534761/
> 
> Are there any outlook that we can support TSX lock elision in musl?

I was involved in the discussions about lock elision on the glibc
mailing list, and from what I could gather, it's a pain to implement
and whether it brings you any benefit is questionable. Before making
any decision, I think we should wait to see some performance figures.

Rich