2017-11-09 18:28+0100, Peter Zijlstra: > On Thu, Nov 09, 2017 at 06:15:11PM +0100, Peter Zijlstra wrote: > > On Thu, Nov 09, 2017 at 06:12:41PM +0100, Peter Zijlstra wrote: > > > On Thu, Nov 09, 2017 at 05:45:23PM +0100, Radim Krcmar wrote: > > > > 2017-11-09 17:17+0100, Peter Zijlstra: > > > > > On Thu, Nov 09, 2017 at 05:05:36PM +0100, Radim Krcmar wrote: > > > > > > 2017-11-09 10:53-0500, Pankaj Gupta: > > > > > > > 2] PV TLB should also behave as per option PV_DEDICATED for better performance. > > > > > > > > > > > > Right, > > > > > > > > > > Shouldn't KVM do flush_tlb_other() in any case? Not sure how > > > > > PV_DEDICATED can help with that. > > > > > > > > It will, the suggestion was based on recent extension of the > > > > flush_tlb_others implementaion, https://lkml.org/lkml/2017/11/8/1146. > > > > > > > > PV_TLB_FLUSH allows a guest to set a flush bit instead of sending flush > > > > IPI if the target VCPU is not running. This would be a waste of time > > > > with PV_DEDICATED as all VCPUs are expected to always running. > > > > > > > > With PV_DEDICATED, the guest should keep using native_flush_tlb_others. > > > > > > Is saving that for_each_cpu() really worth the effort compared to the > > > cost of actually doing the IPIs and CR3 write? > > > > > > Also, you should not put cpumask_t on stack, that's 'broken'. > > > > Also, you'll want to use __cpumask_clear_cpu() there. > > Also^2, that patch split is crazy, after patch 2/3 your machine is > broken due to lost TLB flushes. You have to first add the SHOULD_FLUSH > handling and then clear CPUs from the native_flush_tlb_other() mask. That should be fixed in v2 -- [2/3] must not enable this feature if the host has not exposed it and [3/3] has to expose it. (The ordering of those two doesn't matter as they are separate kernel.)
