Re: [PATCH] sched: introduce configurable delay before entering idle

[Marcelo Tosatti]

On Wed, May 08, 2019 at 12:15:19AM +0200, Peter Zijlstra wrote:
> On Tue, May 07, 2019 at 03:56:49PM -0300, Marcelo Tosatti 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).
> > 
> > This patch introduces a configurable busy-wait delay before entering the
> > architecture delay routine, allowing wakeup IPIs to be skipped 
> > (if the IPI happens in that window).
> > 
> > The real-life workload which this patch improves performance
> > is SAP HANA (by 5-10%) (for which case setting idle_spin to 30 
> > is sufficient).
> > 
> > This patch improves the attached server.py and client.py example 
> > as follows:
> > 
> > Host:                           31.814230202231556
> > Guest:                          38.17718765199993       (83 %)
> > Guest, idle_spin=50us:          33.317709898000004      (95 %)
> > Guest, idle_spin=220us:         32.27826551499999       (98 %)
> > 
> > Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
> 
> Thanks for the CC..
> 
> NAK, this is something that should live in a virt idle governor or
> something along those lines.

Ok, makes sense, will rework the patch!