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Hello,
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.
Regards
--
Julian Anastasov <ja@xxxxxx>
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