Bjoern A. Zeeb wrote:
On Sun, 18 Jun 2006, Sam Leffler wrote:
Andre Oppermann wrote:
andre 2006-06-17 17:57:36 UTC
FreeBSD src repository
Modified files:
sys/netinet tcp_var.h
Log:
Rearrange fields in struct syncache and syncache_head to make them
more
cache line friendly.
Got any benchmarks to back this up? Or perhaps it was just the smiley
face your cache lines gave you :)
The entry chains are traversed quite often and the first thing looked
at is in_conninfo and then sc_rxttime and sc_rxmits. So it makes a
lot of sense to have them close together on the same cache line aligned
to the beginning of the struct and to the native alignment of the
architecture. I did not benchmark it but it is simple reasoning.
That indeed is a good question. From looking at the patch I can see
a new lock introduced while there are other people working on reducing
locking and locking overhead in our network stack trying different
strategies.
>
I hadn't seen a patch or any numbers in this months arch@ or net@
archives (maybe I missed it?).
At the current phase of network stack hacking we should take the
time to get these kind of changes benchmarked under various
loads from different people or at least give them the chance to do
so so nobody can complain afterwards. At least if one wants to
claim performance improvements.
Robert Watson and Paul Saab ran the syncache locking changes in their
testbeds and found 0.7% and 0% regression. The syncache locking will
have its benefits when we deserialize the packet input path. Also the
global tcpinfo lock is held for only a very short amount of time instead
of the whole time.
--
Andre
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