Hi Boris, Thomas, Peter,
On 7/21/22 1:44 PM, Srivatsa S. Bhat wrote:
> From: Srivatsa S. Bhat (VMware) <sriva...@csail.mit.edu>
>
> VMware ESXi allows enabling a passthru mwait CPU-idle state in the
> guest using the following VMX option:
>
> monitor_control.mwait_in_guest = "TRUE"
>
> This lets a vCPU in mwait to remain in guest context (instead of
> yielding to the hypervisor via a 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 ESXi, which
> prevents the hypervisor from running other vCPUs or workloads on the
> corresponding pCPU (particularly when vCPU - pCPU mappings are
> statically defined by the user). [ Note that such a vCPU is not
> actually busy spinning though; it remains in mwait idle state in the
> guest ].
>
> Fix this by overriding the CPU offline play_dead() callback for VMware
> hypervisor, by putting the CPU in halt state (which actually yields to
> the hypervisor), even if mwait support is available.
>
> Signed-off-by: Srivatsa S. Bhat (VMware) <sriva...@csail.mit.edu>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Ingo Molnar <mi...@redhat.com>
> Cc: Borislav Petkov <b...@alien8.de>
> Cc: Dave Hansen <dave.han...@linux.intel.com>
> Cc: "H. Peter Anvin" <h...@zytor.com>
> Cc: Alexey Makhalov <amakha...@vmware.com>
> Cc: Juergen Gross <jgr...@suse.com>
> Cc: x...@kernel.org
> Cc: VMware PV-Drivers Reviewers <pv-driv...@vmware.com>
> ---
Could you share your thoughts on this patch when you get a chance,
please? I verified that this patch still applies cleanly on current
mainline (6.0-rc6). I'm happy to resend the patch though, if it helps.
Thank you!
Regards,
Srivatsa
>
> arch/x86/kernel/cpu/vmware.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
> index c04b933f48d3..420e359ed9bb 100644
> --- a/arch/x86/kernel/cpu/vmware.c
> +++ b/arch/x86/kernel/cpu/vmware.c
> @@ -27,6 +27,7 @@
> #include <linux/clocksource.h>
> #include <linux/cpu.h>
> #include <linux/reboot.h>
> +#include <linux/tboot.h>
> #include <linux/static_call.h>
> #include <asm/div64.h>
> #include <asm/x86_init.h>
> @@ -312,6 +313,21 @@ static int vmware_cpu_down_prepare(unsigned int cpu)
> local_irq_enable();
> return 0;
> }
> +
> +static void vmware_play_dead(void)
> +{
> + play_dead_common();
> + tboot_shutdown(TB_SHUTDOWN_WFS);
> +
> + /*
> + * Put the vCPU going offline in halt instead of mwait (even
> + * if mwait support is available), to make sure that the
> + * offline vCPU yields to the hypervisor (which may not happen
> + * with mwait, for example, if the guest's VMX is configured
> + * to retain the vCPU in guest context upon mwait).
> + */
> + hlt_play_dead();
> +}
> #endif
>
> static __init int activate_jump_labels(void)
> @@ -349,6 +365,7 @@ static void __init vmware_paravirt_ops_setup(void)
> #ifdef CONFIG_SMP
> smp_ops.smp_prepare_boot_cpu =
> vmware_smp_prepare_boot_cpu;
> + smp_ops.play_dead = vmware_play_dead;
> if (cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
> "x86/vmware:online",
> vmware_cpu_online,
>
>
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