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Hi,
A number of the schedulers seem to use an is_overloaded() function that
limits the number of connections to twice the server's weight.
For the sake of discussion I'll be referring to the 2.4.x kernel. We
would be talking about this piece of jewelry:
static inline int is_overloaded(struct ip_vs_dest *dest)
{
if (atomic_read(&dest->activeconns) >
atomic_read(&dest->weight)*2) {
return 1;
}
return 0;
}
And I'm not a bit unsure about the semantics of this is_overloaded
regarding it's mathematical background. Wensong, what was the reason to
arbitraly us twice the amount of activeconns for the overoad criteria?
1. dest->activeconns has such a short life span, it hardly represents
nor reflects the current RS load in any way I could imagine.
2. 2.4.x and 2.6.x differ in what they consider a destination to be
overloaded. IP_VS_DEST_F_OVERLOAD is set when ip_vs_dest_totalconns
exceeds the upper threshold limit and totalconns means currently
active + inactive connections which is also kind of unfortunate. And
yes, there is some more code I haven't mentioned yet.
I'm using
the dh scheduler to balance across 3 machines - once the connections
exceed twice the weight, it refuses new connections from IP addresses that
aren't currently persistent.
What kernel are you talking about, I'm afraid? I've been a bit out of
the loop development wise, so bear with me. And 2.4.x and 2.6.x contain
similar (although not sync'd ... sigh) code regarding this feature:
ratz@webphish:/usr/src/linux-2.6.8-rc2> grep -r is_overloaded *
net/ipv4/ipvs/ip_vs_sh.c:static inline int is_overloaded(struct
ip_vs_dest *dest)
net/ipv4/ipvs/ip_vs_sh.c: || is_overloaded(dest)) {
net/ipv4/ipvs/ip_vs_lblcr.c:is_overloaded(struct ip_vs_dest *dest,
struct ip_vs_service *svc)
net/ipv4/ipvs/ip_vs_lblcr.c: if (!dest || is_overloaded(dest,
svc)) {
net/ipv4/ipvs/ip_vs_dh.c:static inline int is_overloaded(struct
ip_vs_dest *dest)
net/ipv4/ipvs/ip_vs_dh.c: || is_overloaded(dest)) {
net/ipv4/ipvs/ip_vs_lblc.c:is_overloaded(struct ip_vs_dest *dest, struct
ip_vs_service *svc)
net/ipv4/ipvs/ip_vs_lblc.c: || is_overloaded(dest, svc)) {
ratz@webphish:/usr/src/linux-2.6.8-rc2>
ratz@webphish:/usr/src/linux-2.4.27-rc4> grep -r is_overloaded *
net/ipv4/ipvs/ip_vs_sh.c:static inline int is_overloaded(struct
ip_vs_dest *dest)
net/ipv4/ipvs/ip_vs_sh.c: || is_overloaded(dest)) {
net/ipv4/ipvs/ip_vs_lblcr.c:is_overloaded(struct ip_vs_dest *dest,
struct ip_vs_service *svc)
net/ipv4/ipvs/ip_vs_lblcr.c: if (!dest || is_overloaded(dest,
svc)) {
net/ipv4/ipvs/ip_vs_lblc.c:is_overloaded(struct ip_vs_dest *dest, struct
ip_vs_service *svc)
net/ipv4/ipvs/ip_vs_lblc.c: || is_overloaded(dest, svc)) {
net/ipv4/ipvs/ip_vs_dh.c:static inline int is_overloaded(struct
ip_vs_dest *dest)
net/ipv4/ipvs/ip_vs_dh.c: || is_overloaded(dest)) {
ratz@webphish:/usr/src/linux-2.4.27-rc4>
Asymmetric coding :)
This in itself isn't really a problem, but I can't find this behaviour
actually documented anywhere - all the documentation refers to the
weights as being "relative to the other hosts" which means there should
be no difference between me setting the weights on all hosts to 5 or
setting them all to 500.
This is correct. I'm a bit unsure as to what your exact problem is, but
a kernel version would already help, although I believe you're using a
2.4.x kernel. Normally the is_overloaded() function was designed to be
used by the threshold limitation feature only which is only present as a
shacky backport from 2.6.x. I don't quite understand the is_overloaded()
function in the ip_vs_dh scheduler, OTOH, I really haven't been using it
so far.
Expect some followup on this ;)
Take care,
Roberto Nibali, ratz
--
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