Re: [PATCH v2] x86/hotplug: Do not put offline vCPUs in mwait idle state

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 16.01.23 07:01, Srivatsa S. Bhat wrote:
From: "Srivatsa S. Bhat (VMware)" <srivatsa@xxxxxxxxxxxxx>

Under hypervisors that support mwait passthrough, a vCPU in mwait
CPU-idle state remains in guest context (instead of yielding to the
hypervisor via VMEXIT), which helps speed up wakeups from idle.

However, this runs into problems with CPU hotplug, because the Linux
CPU offline path prefers to put the vCPU-to-be-offlined in mwait
state, whenever mwait is available. As a result, since a vCPU in mwait
remains in guest context and does not yield to the hypervisor, an
offline vCPU *appears* to be 100% busy as viewed from the host, which
prevents the hypervisor from running other vCPUs or workloads on the
corresponding pCPU. [ Note that such a vCPU is not actually busy
spinning though; it remains in mwait idle state in the guest ].

Fix this by preventing the use of mwait idle state in the vCPU offline
play_dead() path for any hypervisor, even if mwait support is
available.

Suggested-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Srivatsa S. Bhat (VMware) <srivatsa@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Wyes Karny <wyes.karny@xxxxxxx>
Cc: Lewis Caroll <lewis.carroll@xxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: Alexey Makhalov <amakhalov@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: VMware PV-Drivers Reviewers <pv-drivers@xxxxxxxxxx>
Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
Cc: kvm@xxxxxxxxxxxxxxx
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx

Reviewed-by: Juergen Gross <jgross@xxxxxxxx>


Juergen

Attachment: OpenPGP_0xB0DE9DD628BF132F.asc
Description: OpenPGP public key

Attachment: OpenPGP_signature
Description: OpenPGP digital signature


[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]

  Powered by Linux