[ltt-dev] [PATCH] Poll : introduce poll_wait_exclusive() new function
davidel at xmailserver.org
Wed Nov 26 19:08:11 EST 2008
On Wed, 26 Nov 2008, Mathieu Desnoyers wrote:
> One of the key design rule of LTTng is to do not depend on such
> system-wide data structures, or entity (e.g. single manager thread).
> Everything is per-cpu, and it does scale very well.
> I wonder how badly the approach you propose can scale on large NUMA
> systems, where having to synchronize everything through a single thread
> might become an important point of contention, just due to the cacheline
> bouncing and extra scheduler activity involved.
I dunno the LTT architecture, so I'm staying out of that discussion.
But, if the patch you're trying to push is to avoid thundering herd of so
many threads waiting on the single file*, you've got the same problem
right there. You've got at least the spinlock protecting the queue
where these threads are focusing, whose cacheline is bounced gets bounced
all over the CPUs.
Do you have any measure of the improvements that such poll_wait_exclusive()
will eventually lead to?
More information about the lttng-dev