Re: futex results with dbt-3

Mark Wong wrote:

>Pretty, simple. One to load the database, and 1 to query it. I'll
>attach them.
>
>
>
I've tested it on my dual-cpu computer:
- it works, both cpus run within the postmaster. It seems something your
gentoo setup is broken.
- the number of context switch is down slightly, but not significantly:
The glibc implementation is more or less identical to the implementation
right now in lwlock.c: a spinlock that protects a few variables that are
used to implement the actual mutex, several wait queues: one for
spinlock busy, one or two for the actual mutex code.

Around 25% of the context switches are from spinlock collisions, the
rest are from actual mutex collisions. It might be possible to get rid
of the spinlock collisions by writing a special, futex based semaphore
function that only supports exclusive access [like sem_wait/sem_post],
but I don't think that it's worth the effort: 75% of the context
switches would remain.
What's needed is a buffer manager that can do lookups without a global lock.

--
Manfred