[patch 0/3] cpuidle-haltpoll driver (v2)

From: Marcelo Tosatti <mtosatti@redhat.com>
To: kvm-devel <kvm@vger.kernel.org>
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim KrÄmÃ¡Å™" <rkrcmar@redhat.com>,
	"Andrea Arcangeli" <aarcange@redhat.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Wanpeng Li" <kernellwp@gmail.com>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
	"Raslan KarimAllah" <karahmed@amazon.de>,
	"Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
	"Ankur Arora" <ankur.a.arora@oracle.com>,
	"Christian Borntraeger" <borntraeger@de.ibm.com>
Subject: [patch 0/3] cpuidle-haltpoll driver (v2)
Date: Mon, 03 Jun 2019 19:52:42 -0300	[thread overview]
Message-ID: <20190603225242.289109849@amt.cnet> (raw)

The cpuidle-haltpoll driver allows the guest vcpus to poll for a specified
amount of time before halting. This provides the following benefits
to host side polling:

        1) The POLL flag is set while polling is performed, which allows
           a remote vCPU to avoid sending an IPI (and the associated
           cost of handling the IPI) when performing a wakeup.

        2) The HLT VM-exit cost can be avoided.

The downside of guest side polling is that polling is performed
even with other runnable tasks in the host.

Results comparing halt_poll_ns and server/client application
where a small packet is ping-ponged:

host                                        --> 31.33
halt_poll_ns=300000 / no guest busy spin    --> 33.40   (93.8%)
halt_poll_ns=0 / guest_halt_poll_ns=300000  --> 32.73   (95.7%)

For the SAP HANA benchmarks (where idle_spin is a parameter
of the previous version of the patch, results should be the
same):

hpns == halt_poll_ns

                          idle_spin=0/   idle_spin=800/    idle_spin=0/
                          hpns=200000    hpns=0            hpns=800000
DeleteC06T03 (100 thread) 1.76           1.71 (-3%)        1.78   (+1%)
InsertC16T02 (100 thread) 2.14           2.07 (-3%)        2.18   (+1.8%)
DeleteC00T01 (1 thread)   1.34           1.28 (-4.5%)	   1.29   (-3.7%)
UpdateC00T03 (1 thread)   4.72           4.18 (-12%)	   4.53   (-5%)

V2:

- Move from x86 to generic code (Paolo/Christian).
- Add auto-tuning logic (Paolo).
- Add MSR to disable host side polling (Paolo).