On Wed, 15 May 2019 at 02:20, Marcelo Tosatti <mtosatti@xxxxxxxxxx> wrote: > > On Tue, May 14, 2019 at 11:20:15AM -0400, Konrad Rzeszutek Wilk wrote: > > On Tue, May 14, 2019 at 10:50:23AM -0300, Marcelo Tosatti wrote: > > > On Mon, May 13, 2019 at 05:20:37PM +0800, Wanpeng Li wrote: > > > > On Wed, 8 May 2019 at 02:57, Marcelo Tosatti <mtosatti@xxxxxxxxxx> wrote: > > > > > > > > > > > > > > > Certain workloads perform poorly on KVM compared to baremetal > > > > > due to baremetal's ability to perform mwait on NEED_RESCHED > > > > > bit of task flags (therefore skipping the IPI). > > > > > > > > KVM supports expose mwait to the guest, if it can solve this? > > > > > > > > Regards, > > > > Wanpeng Li > > > > > > Unfortunately mwait in guest is not feasible (uncompatible with multiple > > > guests). Checking whether a paravirt solution is possible. > > > > There is the obvious problem with that the guest can be malicious and > > provide via the paravirt solution bogus data. That is it expose 0% CPU > > usage but in reality be mining and using 100%. > > The idea is to have a hypercall for the guest to perform the > need_resched=1 bit set. It can only hurt itself. This lets me recall the patchset from aliyun https://lkml.org/lkml/2017/6/22/296 They poll after __current_set_polling() in do_idle() so avoid this hypercall I think. Btw, do you get SAP HANA by 5-10% bonus even if adaptive halt-polling is enabled? Regards, Wanpeng Li
