* Nikunj A Dadhania [off-list ref] wrote:

quoted

Here it would massively improve performance - without 
regressing the scheduler code massively.

I tried doing an experiment with the flush_tlb_others_ipi. 
This depends on Raghu's "kvm : Paravirt-spinlock support for 
KVM guests" (https://lkml.org/lkml/2012/1/14/66), which has 
new hypercall for kicking another vcpu out of halt.

  Here are the results from non-PLE hardware. Running ebizzy 
  workload inside the VMs. The table shows the ebizzy score - 
  Records/sec.

  8CPU Intel Xeon, HT disabled, 64 bit VM(8vcpu, 1G RAM)

  +--------+------------+------------+-------------+
  |        |  baseline  |   gang     |   pv_flush  |
  +--------+------------+------------+-------------+
  |   2VM  |   3979.50  |   8818.00  |   11002.50  |
  |   4VM  |   1817.50  |   6236.50  |    6196.75  |
  |   8VM  |    922.12  |   4043.00  |    4001.38  |
  +--------+------------+------------+-------------+

Very nice results!

Seems like the PV approach is massively faster on 2 VMs than 
even the gang scheduling hack, because it attacks the problem
at its root, not just the symptom.

The patch is also an order of magnitude simpler. Gang 
scheduling, R.I.P.

Thanks,

	Ingo