Messages in this thread |  | | Date | Fri, 21 Jan 2011 19:32:08 +0530 | From | Srivatsa Vaddagiri <> | Subject | Re: [PATCH 2/3] kvm hypervisor : Add hypercalls to support pv-ticketlock |
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On Thu, Jan 20, 2011 at 09:56:27AM -0800, Jeremy Fitzhardinge wrote: > > The key here is not to > > sleep when waiting for locks (as implemented by current patch-series, which can > > put other VMs at an advantage by giving them more time than they are entitled > > to) > > Why? If a VCPU can't make progress because its waiting for some > resource, then why not schedule something else instead?
In the process, "something else" can get more share of cpu resource than its entitled to and that's where I was bit concerned. I guess one could employ hard-limits to cap "something else's" bandwidth where it is of real concern (like clouds).
> Presumably when > the VCPU does become runnable, the scheduler will credit its previous > blocked state and let it run in preference to something else.
which may not be sufficient for it to gain back bandwidth lost while blocked (speaking of mainline scheduler atleast).
> > Is there a way we can dynamically expand the size of lock only upon contention > > to include additional information like owning vcpu? Have the lock point to a > > per-cpu area upon contention where additional details can be stored perhaps? > > As soon as you add a pointer to the lock, you're increasing its size.
I didn't really mean to expand size statically. Rather have some bits of the lock word store pointer to a per-cpu area when there is contention (somewhat similar to how bits of rt_mutex.owner are used). I haven't thought thr' this in detail to see if that is possible though.
- vatsa
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