| Message ID | 1613119176-20864-2-git-send-email-pmorel@linux.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: s390: diag9c forwarding | expand |
On 2/12/21 9:39 AM, Pierre Morel wrote: > When we receive intercept a DIAG_9C from the guest we verify > that the target real CPU associated with the virtual CPU > designated by the guest is running and if not we forward the > DIAG_9C to the target real CPU. > > To avoid a diag9c storm we allow a maximal rate of diag9c forwarding. > > The rate is calculated as a count per second defined as a > new parameter of the s390 kvm module: diag9c_forwarding_hz . > > The default value is to not forward diag9c. > > Signed-off-by: Pierre Morel <pmorel@linux.ibm.com> > --- > Documentation/virt/kvm/s390-diag.rst | 33 ++++++++++++++++++++++++++++ > arch/s390/include/asm/kvm_host.h | 1 + > arch/s390/include/asm/smp.h | 1 + > arch/s390/kernel/smp.c | 1 + > arch/s390/kvm/diag.c | 31 +++++++++++++++++++++++--- > arch/s390/kvm/kvm-s390.c | 6 +++++ > arch/s390/kvm/kvm-s390.h | 8 +++++++ > 7 files changed, 78 insertions(+), 3 deletions(-) > > diff --git a/Documentation/virt/kvm/s390-diag.rst b/Documentation/virt/kvm/s390-diag.rst > index eaac4864d3d6..a6371bc4ea90 100644 > --- a/Documentation/virt/kvm/s390-diag.rst > +++ b/Documentation/virt/kvm/s390-diag.rst > @@ -84,3 +84,36 @@ If the function code specifies 0x501, breakpoint functions may be performed. > This function code is handled by userspace. > > This diagnose function code has no subfunctions and uses no parameters. > + > + > +DIAGNOSE function code 'X'9C - Voluntary Time Slice Yield > +--------------------------------------------------------- > + > +General register 1 contains the target CPU address. > + > +In a guest of a hypervisor like LPAR, KVM or z/VM using shared host CPUs, > +DIAGNOSE with function code 'X'9C may improve system performance by > +yielding the host CPU on which the guest CPU is running to be assigned > +to another guest CPU, preferably the logical CPU containing the specified > +target CPU. > + > + > +DIAG 'X'9C forwarding > ++++++++++++++++++++++ > + > +Under KVM, the guest operating system may send a DIAGNOSE code 'X'9C to > +the host when it fails to acquire a spinlock for a virtual CPU > +and detects that the host CPU on which the virtual guest CPU owner is > +assigned to is not running to try to get this host CPU running and > +consequently the guest virtual CPU running and freeing the lock. > + > +However, on the logical partition the real CPU on which the previously > +targeted host CPU is assign may itself not be running. > +By forwarding the DIAGNOSE code 'X'9C, initially sent by the guest, > +from the host to LPAR hypervisor, this one will hopefully schedule > +the host CPU which will let KVM run the target guest CPU. > + > +diag9c_forwarding_hz > + KVM kernel parameter allowing to specify the maximum number of DIAGNOSE > + 'X'9C forwarding per second in the purpose of avoiding a DIAGNOSE 'X'9C > + forwarding storm. > diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h > index 527776a1f076..cb19508c22fb 100644 > --- a/arch/s390/include/asm/kvm_host.h > +++ b/arch/s390/include/asm/kvm_host.h > @@ -456,6 +456,7 @@ struct kvm_vcpu_stat { > u64 diagnose_44; > u64 diagnose_9c; > u64 diagnose_9c_ignored; > + u64 diagnose_9c_forward; > u64 diagnose_258; > u64 diagnose_308; > u64 diagnose_500; > diff --git a/arch/s390/include/asm/smp.h b/arch/s390/include/asm/smp.h > index 01e360004481..e317fd4866c1 100644 > --- a/arch/s390/include/asm/smp.h > +++ b/arch/s390/include/asm/smp.h > @@ -63,5 +63,6 @@ extern void __noreturn cpu_die(void); > extern void __cpu_die(unsigned int cpu); > extern int __cpu_disable(void); > extern void schedule_mcck_handler(void); > +void notrace smp_yield_cpu(int cpu); > > #endif /* __ASM_SMP_H */ > diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c > index 27c763014114..15e207a671fd 100644 > --- a/arch/s390/kernel/smp.c > +++ b/arch/s390/kernel/smp.c > @@ -422,6 +422,7 @@ void notrace smp_yield_cpu(int cpu) > asm volatile("diag %0,0,0x9c" > : : "d" (pcpu_devices[cpu].address)); > } > +EXPORT_SYMBOL(smp_yield_cpu); > > /* > * Send cpus emergency shutdown signal. This gives the cpus the > diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c > index 5b8ec1c447e1..34cf41fa6fa2 100644 > --- a/arch/s390/kvm/diag.c > +++ b/arch/s390/kvm/diag.c > @@ -150,6 +150,19 @@ static int __diag_time_slice_end(struct kvm_vcpu *vcpu) > return 0; > } > > +static unsigned int forward_cnt; > +static unsigned long cur_slice; > + > +static int diag9c_forwarding_overrun(void) > +{ > + /* Reset the count on a new slice */ > + if (time_after(jiffies, cur_slice)) { > + cur_slice = jiffies; > + forward_cnt = diag9c_forwarding_hz / HZ; > + } > + return forward_cnt-- ? 1 : 0; /o\ seems a "<= 0 " has been forgotten here I send the update asap. regards, Pierre
diff --git a/Documentation/virt/kvm/s390-diag.rst b/Documentation/virt/kvm/s390-diag.rst index eaac4864d3d6..a6371bc4ea90 100644 --- a/Documentation/virt/kvm/s390-diag.rst +++ b/Documentation/virt/kvm/s390-diag.rst @@ -84,3 +84,36 @@ If the function code specifies 0x501, breakpoint functions may be performed. This function code is handled by userspace. This diagnose function code has no subfunctions and uses no parameters. + + +DIAGNOSE function code 'X'9C - Voluntary Time Slice Yield +--------------------------------------------------------- + +General register 1 contains the target CPU address. + +In a guest of a hypervisor like LPAR, KVM or z/VM using shared host CPUs, +DIAGNOSE with function code 'X'9C may improve system performance by +yielding the host CPU on which the guest CPU is running to be assigned +to another guest CPU, preferably the logical CPU containing the specified +target CPU. + + +DIAG 'X'9C forwarding ++++++++++++++++++++++ + +Under KVM, the guest operating system may send a DIAGNOSE code 'X'9C to +the host when it fails to acquire a spinlock for a virtual CPU +and detects that the host CPU on which the virtual guest CPU owner is +assigned to is not running to try to get this host CPU running and +consequently the guest virtual CPU running and freeing the lock. + +However, on the logical partition the real CPU on which the previously +targeted host CPU is assign may itself not be running. +By forwarding the DIAGNOSE code 'X'9C, initially sent by the guest, +from the host to LPAR hypervisor, this one will hopefully schedule +the host CPU which will let KVM run the target guest CPU. + +diag9c_forwarding_hz + KVM kernel parameter allowing to specify the maximum number of DIAGNOSE + 'X'9C forwarding per second in the purpose of avoiding a DIAGNOSE 'X'9C + forwarding storm. diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h index 527776a1f076..cb19508c22fb 100644 --- a/arch/s390/include/asm/kvm_host.h +++ b/arch/s390/include/asm/kvm_host.h @@ -456,6 +456,7 @@ struct kvm_vcpu_stat { u64 diagnose_44; u64 diagnose_9c; u64 diagnose_9c_ignored; + u64 diagnose_9c_forward; u64 diagnose_258; u64 diagnose_308; u64 diagnose_500; diff --git a/arch/s390/include/asm/smp.h b/arch/s390/include/asm/smp.h index 01e360004481..e317fd4866c1 100644 --- a/arch/s390/include/asm/smp.h +++ b/arch/s390/include/asm/smp.h @@ -63,5 +63,6 @@ extern void __noreturn cpu_die(void); extern void __cpu_die(unsigned int cpu); extern int __cpu_disable(void); extern void schedule_mcck_handler(void); +void notrace smp_yield_cpu(int cpu); #endif /* __ASM_SMP_H */ diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c index 27c763014114..15e207a671fd 100644 --- a/arch/s390/kernel/smp.c +++ b/arch/s390/kernel/smp.c @@ -422,6 +422,7 @@ void notrace smp_yield_cpu(int cpu) asm volatile("diag %0,0,0x9c" : : "d" (pcpu_devices[cpu].address)); } +EXPORT_SYMBOL(smp_yield_cpu); /* * Send cpus emergency shutdown signal. This gives the cpus the diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c index 5b8ec1c447e1..34cf41fa6fa2 100644 --- a/arch/s390/kvm/diag.c +++ b/arch/s390/kvm/diag.c @@ -150,6 +150,19 @@ static int __diag_time_slice_end(struct kvm_vcpu *vcpu) return 0; } +static unsigned int forward_cnt; +static unsigned long cur_slice; + +static int diag9c_forwarding_overrun(void) +{ + /* Reset the count on a new slice */ + if (time_after(jiffies, cur_slice)) { + cur_slice = jiffies; + forward_cnt = diag9c_forwarding_hz / HZ; + } + return forward_cnt-- ? 1 : 0; +} + static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu) { struct kvm_vcpu *tcpu; @@ -167,9 +180,21 @@ static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu) if (!tcpu) goto no_yield; - /* target already running */ - if (READ_ONCE(tcpu->cpu) >= 0) - goto no_yield; + /* target guest VCPU already running */ + if (READ_ONCE(tcpu->cpu) >= 0) { + if (!diag9c_forwarding_hz || diag9c_forwarding_overrun()) + goto no_yield; + + /* target host CPU already running */ + if (!vcpu_is_preempted(tcpu->cpu)) + goto no_yield; + smp_yield_cpu(tcpu->cpu); + VCPU_EVENT(vcpu, 5, + "diag time slice end directed to %d: yield forwarded", + tid); + vcpu->stat.diagnose_9c_forward++; + return 0; + } if (kvm_vcpu_yield_to(tcpu) <= 0) goto no_yield; diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 053ef36784e4..c23e22610a89 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -157,6 +157,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = { VCPU_STAT("instruction_diag_44", diagnose_44), VCPU_STAT("instruction_diag_9c", diagnose_9c), VCPU_STAT("diag_9c_ignored", diagnose_9c_ignored), + VCPU_STAT("diag_9c_forward", diagnose_9c_forward), VCPU_STAT("instruction_diag_258", diagnose_258), VCPU_STAT("instruction_diag_308", diagnose_308), VCPU_STAT("instruction_diag_500", diagnose_500), @@ -190,6 +191,11 @@ static bool use_gisa = true; module_param(use_gisa, bool, 0644); MODULE_PARM_DESC(use_gisa, "Use the GISA if the host supports it."); +/* maximum diag9c forwarding per second */ +unsigned int diag9c_forwarding_hz; +module_param(diag9c_forwarding_hz, uint, 0644); +MODULE_PARM_DESC(diag9c_forwarding_hz, "Maximum diag9c forwarding per second"); + /* * For now we handle at most 16 double words as this is what the s390 base * kernel handles and stores in the prefix page. If we ever need to go beyond diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h index 79dcd647b378..9fad25109b0d 100644 --- a/arch/s390/kvm/kvm-s390.h +++ b/arch/s390/kvm/kvm-s390.h @@ -471,4 +471,12 @@ void kvm_s390_reinject_machine_check(struct kvm_vcpu *vcpu, * @kvm: the KVM guest */ void kvm_s390_vcpu_crypto_reset_all(struct kvm *kvm); + +/** + * diag9c_forwarding_hz + * + * Set the maximum number of diag9c forwarding per second + */ +extern unsigned int diag9c_forwarding_hz; + #endif
When we receive intercept a DIAG_9C from the guest we verify that the target real CPU associated with the virtual CPU designated by the guest is running and if not we forward the DIAG_9C to the target real CPU. To avoid a diag9c storm we allow a maximal rate of diag9c forwarding. The rate is calculated as a count per second defined as a new parameter of the s390 kvm module: diag9c_forwarding_hz . The default value is to not forward diag9c. Signed-off-by: Pierre Morel <pmorel@linux.ibm.com> --- Documentation/virt/kvm/s390-diag.rst | 33 ++++++++++++++++++++++++++++ arch/s390/include/asm/kvm_host.h | 1 + arch/s390/include/asm/smp.h | 1 + arch/s390/kernel/smp.c | 1 + arch/s390/kvm/diag.c | 31 +++++++++++++++++++++++--- arch/s390/kvm/kvm-s390.c | 6 +++++ arch/s390/kvm/kvm-s390.h | 8 +++++++ 7 files changed, 78 insertions(+), 3 deletions(-)