Re: Fine-grained locking for POSIX local sockets (UNIX domain sockets)

On Wednesday 10 May 2006 02:23, Kris Kennaway wrote:
There are at least several issues here:

* Factor of >two difference in performance across the board (all
loads) relative to Linux. This may be general issues like
gettimeofday() on Linux vs FreeBSD; clearly there is something *very
big* to blame here. Mysql does do *lots* of such calls, so the cost
of them is surely a component in performance, the only question is if
it's the main one.

My last recall is that gettimeofday is not a syscall on Linux, they called
it vgettimeofday, they also have a lower overhead syscall: vsyscall which
uses sysenter/sysexit when CPU supports, they do calculation in userland,
the page is exported by kernel which can be executed by userland.
at least I saw the idea on one serious hacker's blog, but now I can not find
the URL.

* When you get some of the locking out of the way (per this thread)
FreeBSD has 44% better peak performance on Sven's test on amd64, but
tails off by about 33% at higher loads compared to unpatched. I see
similar changes on 12-CPU E4500, but not as much performance gain (may
be due to other reasons). i.e. optimizing the locking allows a new,
bigger bottleneck to suck on center stage. This is the basis for my
observation about libthr at high loads. It is not the same as the
above issue.

Kris

Fixing one of big lock contentions is not enough, you have to fix them
all, it is easy to see that a second contention becomes a top one. :-)

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