2017-11-10 1:15 GMT+08:00 Peter Zijlstra <peterz@xxxxxxxxxxxxx>: > 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'. Thanks pointing out this. I found a useful comments in arch/x86/kernel/irq.c: /* These two declarations are only used in check_irq_vectors_for_cpu_disable() * below, which is protected by stop_machine(). Putting them on the stack * results in a stack frame overflow. Dynamically allocating could result in a * failure so declare these two cpumasks as global. */ static struct cpumask affinity_new, online_new; > > Also, you'll want to use __cpumask_clear_cpu() there. Will do. Regards, Wanpeng Li
