Srivatsa S. Bhat
2022-Jul-21 20:44 UTC
[PATCH] smp/hotplug, x86/vmware: Put offline vCPUs in halt instead of mwait
From: Srivatsa S. Bhat (VMware) <srivatsa at 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) <srivatsa at csail.mit.edu>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Ingo Molnar <mingo at redhat.com>
Cc: Borislav Petkov <bp at alien8.de>
Cc: Dave Hansen <dave.hansen at linux.intel.com>
Cc: "H. Peter Anvin" <hpa at zytor.com>
Cc: Alexey Makhalov <amakhalov at vmware.com>
Cc: Juergen Gross <jgross at suse.com>
Cc: x86 at kernel.org
Cc: VMware PV-Drivers Reviewers <pv-drivers at vmware.com>
---
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,
Srivatsa S. Bhat
2022-Sep-23 01:57 UTC
[PATCH] smp/hotplug, x86/vmware: Put offline vCPUs in halt instead of mwait
Hi Boris, Thomas, Peter, On 7/21/22 1:44 PM, Srivatsa S. Bhat wrote:> From: Srivatsa S. Bhat (VMware) <srivatsa at 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) <srivatsa at csail.mit.edu> > Cc: Thomas Gleixner <tglx at linutronix.de> > Cc: Peter Zijlstra <peterz at infradead.org> > Cc: Ingo Molnar <mingo at redhat.com> > Cc: Borislav Petkov <bp at alien8.de> > Cc: Dave Hansen <dave.hansen at linux.intel.com> > Cc: "H. Peter Anvin" <hpa at zytor.com> > Cc: Alexey Makhalov <amakhalov at vmware.com> > Cc: Juergen Gross <jgross at suse.com> > Cc: x86 at kernel.org > Cc: VMware PV-Drivers Reviewers <pv-drivers at 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, > >
Peter Zijlstra
2022-Sep-23 07:05 UTC
[PATCH] smp/hotplug, x86/vmware: Put offline vCPUs in halt instead of mwait
On Thu, Jul 21, 2022 at 01:44:33PM -0700, Srivatsa S. Bhat wrote:> From: Srivatsa S. Bhat (VMware) <srivatsa at 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).I would hope vCPU pinning is a mandatory thing when MWAIT passthrough it set?> [ 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) <srivatsa at csail.mit.edu> > ---> +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,No real objection here; but would not something like the below fix the problem more generally? I'm thinking MWAIT passthrough for *any* hypervisor doesn't want play_dead to use it. diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index f24227bc3220..166cb3aaca8a 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -1759,6 +1759,8 @@ static inline void mwait_play_dead(void) return; if (!this_cpu_has(X86_FEATURE_CLFLUSH)) return; + if (this_cpu_has(X86_FEATURE_HYPERVISOR)) + return; if (__this_cpu_read(cpu_info.cpuid_level) < CPUID_MWAIT_LEAF) return;