RFR: 8079315: UseCondCardMark broken in conjunction with CMS precleaning

[Andrew Haley]

On 05/11/2015 05:06 PM, Vitaly Davidovich wrote:

>> Also the global operation is not purely, but “mostly" locally expensive
>> for the thread performing the global fence. The cost on global CPUs is
>> pretty much simply a normal fence (roughly). Of course there is always
>> gonna be that one guy with 4000 CPUs which might be a bit awkward.

Well yes, but that guy with 4000 CPUs is precisely the target for
UseCondCardMark.

>> But even then, with high enough n, shared, timestamped global
>> fences etc, even such ridiculous scalability should be within
>> reach.
> 
> Is it roughly like a normal fence for remote CPUs?

I would not think so.  Surely you'd have to interrupt every core in
the process and do a bunch of flushes.  A TLB flush is expensive, as
is interrupting the core itself.  I'm fairly sure there's no way to
flush a remote core's TLB without interrupting it.

Andrew.