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SubjectRe: [PATCH] sched: introduce configurable delay before entering idle
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@redhat.com>

Thanks for the CC..

NAK, this is something that should live in a virt idle governor or
something along those lines.

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