On Tue, Jul 30, 2019 at 05:33:55PM +0800, Wanpeng Li wrote: > From: Wanpeng Li <[email protected]> > > Wake-affine is a feature inside scheduler which we attempt to make processes > running closely, it gains benefit mostly from cache-hit. When waker tries > to wakup wakee, it needs to select cpu to run wakee, wake affine heuristic > mays select the cpu which waker is running on currently instead of the prev > cpu which wakee was last time running. > > However, in multiple VMs over-subscribe virtualization scenario, it increases > the probability to incur vCPU stacking which means that the sibling vCPUs > from > the same VM will be stacked on one pCPU. I test three 80 vCPUs VMs running on > one 80 pCPUs Skylake server(PLE is supported), the ebizzy score can increase > 17% > after disabling wake-affine for vCPU process. > > When qemu/other vCPU inject virtual interrupt to guest through waking up one > sleeping vCPU, it increases the probability to stack vCPUs/qemu by scheduler > wake-affine. vCPU stacking issue can greately inceases the lock > synchronization > latency in a virtualized environment. This patch disables wake-affine vCPU > process to mitigtate lock holder preemption. > > Cc: Peter Zijlstra <[email protected]> > Cc: Thomas Gleixner <[email protected]> > Cc: Paolo Bonzini <[email protected]> > Cc: Radim Krčmář <[email protected]> > Signed-off-by: Wanpeng Li <[email protected]> > --- > include/linux/sched.h | 1 + > kernel/sched/fair.c | 3 +++ > virt/kvm/kvm_main.c | 1 + > 3 files changed, 5 insertions(+)
> index 036be95..18eb1fa 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -5428,6 +5428,9 @@ static int wake_wide(struct task_struct *p) > unsigned int slave = p->wakee_flips; > int factor = this_cpu_read(sd_llc_size); > > + if (unlikely(p->flags & PF_NO_WAKE_AFFINE)) > + return 1; > + > if (master < slave) > swap(master, slave); > if (slave < factor || master < slave * factor) I intensely dislike how you misrepresent this patch as a KVM patch. Also the above is very much not the right place, even if this PF_flag were to live.
