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Hello,
On Sat, 13 Apr 2013, Julian Anastasov wrote:
> On Fri, 12 Apr 2013, Simon Kirby wrote:
>
> > Hello!
> >
> > We use lblc in some environments to try to maintain some cache locality.
> >
> > We recently had some problems upgrading beyond 2.6.38 in one environment.
> > The cluster kept overloading real servers and showed flapping that didn't
> > occur on 2.6.38 and older. I was never able to figure this out, but I
> > think now I see the reason.
> >
> > We need to use fairly high weights, since lblc requires this in order to
> > do rescheduling in the event of overload. In the event that we have 3000
> > activeconns to a real server and a weight of 3000, the next connection
> > will check to see if any other real server has 2*activeconns less than
> > its weight, and if so, reschedule by wlc.
> >
> > With b552f7e3a9524abcbcdf86f0a99b2be58e55a9c6, which "git tag --contains"
> > says appeared in 2.6.39-rc, the open-coded activeconns * 50 + inactconns
> > was changed to ip_vs_dest_conn_overhead() that matches the implementation
> > in ip_vs_wlc.c and others. The problem for us is that ip_vs_lblc.c uses
> > "int" (and wlc uses "unsigned int") for "loh" and "doh" variables that
> > the ip_vs_dest_conn_overhead() result is stored in, and then these are
> > multiplied by the weight.
> >
> > ip_vs_dest_conn_overhead() uses (activeconns << 8) + inactconns (* 256
> > instead of * 50), so before where 3000 * 3000 * 50 would fit in an int,
> > 3000 * 3000 * 256 does not.
>
> There is no big difference between 50 and 256.
>
> > We really don't care about inactconns, so removing the "<< 8" and just
> > using activeconns would work for us, but I suspect it must be there for a
> > raeason. "unsigned long" would fix the problem only for 64-bit arches.
> > Using __u64 would work everywhere, but perhaps be slow on 32-bit arches.
> > Thoughts?
>
> May be we can avoid 64-bit multiply with a
> 32*32=>64 optimization, for example:
>
> - if (loh * atomic_read(&dest->weight) >
> - doh * atomic_read(&least->weight)) {
> + if ((__u64) loh * atomic_read(&dest->weight) >
> + (__u64) doh * atomic_read(&least->weight)) {
>
> May be __s64/__u64 does not matter here. Can you
> create and test such patch for lblc and lblcr against
> ipvs-next or net-next tree? Such change should be also
> applied to other schedulers but it does not look so critical.
Any progress on this problem?
Regards
--
Julian Anastasov <ja@xxxxxx>
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