[Qemu-devel] [PATCH v2 0/2] Small fixes for SMT guests in Power9

[Qemu-devel] [PATCH v2 0/2] Small fixes for SMT guests in Power9

[Jose Ricardo Ziviani]

v2:
 - divided in two patches:
    (1) enables smt8 mode to P9 guests
    (2) checks if host supports the # of threads/core required
        limitation: doesn't check guest running in compat mode

This patchset contains 2 changes:

(1) A P9 guest defined like -smp sockets=1,cores=1,threads=8 will be silently
changed to threads=4:

(guest) # lscpu
Architecture:          ppc64le
Byte Order:            Little Endian
CPU(s):                4
On-line CPU(s) list:   0-3
Thread(s) per core:    4
Core(s) per socket:    1
Socket(s):             1
NUMA node(s):          1
...
(qemu) info cpus
* CPU #0: nip=0xc0000000000db9cc thread_id=9440
  CPU #1: nip=0xc0000000000db9cc thread_id=9441
  CPU #2: nip=0xc0000000000db9cc thread_id=9442
  CPU #3: nip=0xc0000000000db9cc thread_id=9443
  CPU #4: nip=0x0000000000000100 (halted) thread_id=9444
  CPU #5: nip=0x0000000000000100 (halted) thread_id=9445
  CPU #6: nip=0x0000000000000100 (halted) thread_id=9446
  CPU #7: nip=0x0000000000000100 (halted) thread_id=9447

This patch enables P9 guests to use emulated smt because KVM supports it:

(guest) # lscpu
Architecture:          ppc64le
Byte Order:            Little Endian
CPU(s):                8
On-line CPU(s) list:   0-7
Thread(s) per core:    8
Core(s) per socket:    1
Socket(s):             1
NUMA node(s):          1

(qemu) info cpus
* CPU #0: nip=0xc0000000000d30ac thread_id=68400
  CPU #1: nip=0xc0000000000d30ac thread_id=68401
  CPU #2: nip=0xc0000000000d30ac thread_id=68402
  CPU #3: nip=0xc0000000000d30ac thread_id=68403
  CPU #4: nip=0xc0000000000d30ac thread_id=68404
  CPU #5: nip=0xc0000000000d30ac thread_id=68405
  CPU #6: nip=0xc0000000000d30ac thread_id=68406
  CPU #7: nip=0xc0000000000d30ac thread_id=68407

CPU hotplugging also works as expected:

(qemu) device_add host-spapr-cpu-core,id=core8,core-id=8
(qemu) info cpus
* CPU #0: nip=0xc0000000000d30ac thread_id=68400
  CPU #1: nip=0xc0000000000d30ac thread_id=68401
  CPU #2: nip=0xc0000000000d30ac thread_id=68402
  CPU #3: nip=0xc0000000000d30ac thread_id=68403
  CPU #4: nip=0xc0000000000d30ac thread_id=68404
  CPU #5: nip=0xc0000000000d30ac thread_id=68405
  CPU #6: nip=0xc0000000000d30ac thread_id=68406
  CPU #7: nip=0xc0000000000d30ac thread_id=68407
  CPU #8: nip=0xc0000000000d30ac thread_id=68492
  CPU #9: nip=0xc0000000000d30ac thread_id=68493
  CPU #10: nip=0xc0000000000d30ac thread_id=68494
  CPU #11: nip=0xc0000000000d30ac thread_id=68495
  CPU #12: nip=0xc0000000000d30ac thread_id=68496
  CPU #13: nip=0xc0000000000d30ac thread_id=68497
  CPU #14: nip=0xc0000000000d30ac thread_id=68498
  CPU #15: nip=0xc0000000000d30ac thread_id=68499

(guest) # lscpu
Architecture:          ppc64le
Byte Order:            Little Endian
CPU(s):                16
On-line CPU(s) list:   0-15
Thread(s) per core:    8
Core(s) per socket:    2
Socket(s):             1
NUMA node(s):          1

(2) Checks if KVM supports the number of threads required

If users try to pass more threads/core than the host supports it displays an
error message and quits:

qemu-system-ppc64: KVM does not support 8 threads/core.
Available VSMT modes: 4 2 1.

Jose Ricardo Ziviani (2):
  ppc: Change Power9 compat table to support at most 8 threads/core
  ppc: spapr: Check if thread argument is supported by host KVM

 hw/ppc/spapr.c       | 10 ++++++++++
 target/ppc/compat.c  |  2 +-
 target/ppc/kvm.c     |  5 +++++
 target/ppc/kvm_ppc.h |  6 ++++++
 4 files changed, 22 insertions(+), 1 deletion(-)

-- 
2.14.3

[Qemu-devel] [PATCH v2 1/2] ppc: Change Power9 compat table to support at most 8 threads/core

[Jose Ricardo Ziviani]

Increases the max smt mode to 8 for Power9. That's because KVM supports
smt emulation in this platform so QEMU should allow users to use it as
well.

Today if we try to pass -smp ...,threads=8, QEMU will silently truncate
it to smt4 mode and may cause a crash if we try to perform a cpu
hotplug.

Signed-off-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
---
 target/ppc/compat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target/ppc/compat.c b/target/ppc/compat.c
index ad8f93c064..d1770cdc6f 100644
--- a/target/ppc/compat.c
+++ b/target/ppc/compat.c
@@ -73,7 +73,7 @@ static const CompatInfo compat_table[] = {
         .pvr = CPU_POWERPC_LOGICAL_3_00,
         .pcr = PCR_COMPAT_3_00,
         .pcr_level = PCR_COMPAT_3_00,
-        .max_threads = 4,
+        .max_threads = 8,
     },
 };
 
-- 
2.14.3

Re: [Qemu-devel] [PATCH v2 1/2] ppc: Change Power9 compat table to support at most 8 threads/core

[David Gibson]

[-- Attachment #1: Type: text/plain, Size: 1274 bytes --]

On Sun, Jan 14, 2018 at 05:23:48PM -0200, Jose Ricardo Ziviani wrote:
> Increases the max smt mode to 8 for Power9. That's because KVM supports
> smt emulation in this platform so QEMU should allow users to use it as
> well.
> 
> Today if we try to pass -smp ...,threads=8, QEMU will silently truncate
> it to smt4 mode and may cause a crash if we try to perform a cpu
> hotplug.
> 
> Signed-off-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>

Applied, with the addition of a comment explaining why we want this
despite the hardware limit.

> ---
>  target/ppc/compat.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/target/ppc/compat.c b/target/ppc/compat.c
> index ad8f93c064..d1770cdc6f 100644
> --- a/target/ppc/compat.c
> +++ b/target/ppc/compat.c
> @@ -73,7 +73,7 @@ static const CompatInfo compat_table[] = {
>          .pvr = CPU_POWERPC_LOGICAL_3_00,
>          .pcr = PCR_COMPAT_3_00,
>          .pcr_level = PCR_COMPAT_3_00,
> -        .max_threads = 4,
> +        .max_threads = 8,
>      },
>  };
>  

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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[Qemu-devel] [PATCH v2 2/2] ppc: spapr: Check if thread argument is supported by host KVM

[Jose Ricardo Ziviani]

QEMU currently checks whether SMT passed is valid or not. However, it
doesn't check if KVM supports such mode when kvm is enabled.

This patch relies on KVM_CAP_PPC_SMT_POSSIBLE to make it sure that QEMU
will either set a valid SMT mode or warn an error message and quit.

Signed-off-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
---
 hw/ppc/spapr.c       | 10 ++++++++++
 target/ppc/kvm.c     |  5 +++++
 target/ppc/kvm_ppc.h |  6 ++++++
 3 files changed, 21 insertions(+)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index d1acfe8858..aed4d25fc4 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -2261,12 +2261,22 @@ static void spapr_set_vsmt_mode(sPAPRMachineState *spapr, Error **errp)
                      "on a pseries machine");
         goto out;
     }
+
     if (!is_power_of_2(smp_threads)) {
         error_setg(&local_err, "Cannot support %d threads/core on a pseries "
                      "machine because it must be a power of 2", smp_threads);
         goto out;
     }
 
+    if (kvm_enabled() && kvmppc_cap_smt_possible() > 0) {
+        if ((kvmppc_cap_smt_possible() & smp_threads) != smp_threads) {
+            error_setg(&local_err, "KVM does not support %d threads/core.",
+                    smp_threads);
+            kvmppc_hint_smt_possible(&local_err);
+            goto out;
+        }
+    }
+
     /* Detemine the VSMT mode to use: */
     if (vsmt_user) {
         if (spapr->vsmt < smp_threads) {
diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
index 914be687e7..4a8ff4d63c 100644
--- a/target/ppc/kvm.c
+++ b/target/ppc/kvm.c
@@ -2456,6 +2456,11 @@ bool kvmppc_has_cap_mmu_hash_v3(void)
     return cap_mmu_hash_v3;
 }
 
+int kvmppc_cap_smt_possible(void)
+{
+    return cap_ppc_smt_possible;
+}
+
 PowerPCCPUClass *kvm_ppc_get_host_cpu_class(void)
 {
     uint32_t host_pvr = mfpvr();
diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h
index ecb55493cc..2221850723 100644
--- a/target/ppc/kvm_ppc.h
+++ b/target/ppc/kvm_ppc.h
@@ -59,6 +59,7 @@ bool kvmppc_has_cap_fixup_hcalls(void);
 bool kvmppc_has_cap_htm(void);
 bool kvmppc_has_cap_mmu_radix(void);
 bool kvmppc_has_cap_mmu_hash_v3(void);
+int kvmppc_cap_smt_possible(void);
 int kvmppc_enable_hwrng(void);
 int kvmppc_put_books_sregs(PowerPCCPU *cpu);
 PowerPCCPUClass *kvm_ppc_get_host_cpu_class(void);
@@ -290,6 +291,11 @@ static inline bool kvmppc_has_cap_mmu_hash_v3(void)
     return false;
 }
 
+static inline int kvmppc_cap_smt_possible(void)
+{
+    return 0;
+}
+
 static inline int kvmppc_enable_hwrng(void)
 {
     return -1;
-- 
2.14.3

Re: [Qemu-devel] [PATCH v2 2/2] ppc: spapr: Check if thread argument is supported by host KVM

[David Gibson]

[-- Attachment #1: Type: text/plain, Size: 3553 bytes --]

On Sun, Jan 14, 2018 at 05:23:49PM -0200, Jose Ricardo Ziviani wrote:
> QEMU currently checks whether SMT passed is valid or not. However, it
> doesn't check if KVM supports such mode when kvm is enabled.

That's not really true - the attempt to actually set the vsmt mode in
KVM later on in spapr_set_vsmt_mode() will fail if KVM can't support
the number of threads.

The error added here might be a bit easier to understand, since it
doesn't refer to vsmt modes, which might just confuse the issue.

The change isn't urgent, though.

> This patch relies on KVM_CAP_PPC_SMT_POSSIBLE to make it sure that QEMU
> will either set a valid SMT mode or warn an error message and quit.
> 
> Signed-off-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
> ---
>  hw/ppc/spapr.c       | 10 ++++++++++
>  target/ppc/kvm.c     |  5 +++++
>  target/ppc/kvm_ppc.h |  6 ++++++
>  3 files changed, 21 insertions(+)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index d1acfe8858..aed4d25fc4 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -2261,12 +2261,22 @@ static void spapr_set_vsmt_mode(sPAPRMachineState *spapr, Error **errp)
>                       "on a pseries machine");
>          goto out;
>      }
> +
>      if (!is_power_of_2(smp_threads)) {
>          error_setg(&local_err, "Cannot support %d threads/core on a pseries "
>                       "machine because it must be a power of 2", smp_threads);
>          goto out;
>      }
>  
> +    if (kvm_enabled() && kvmppc_cap_smt_possible() > 0) {
> +        if ((kvmppc_cap_smt_possible() & smp_threads) != smp_threads) {
> +            error_setg(&local_err, "KVM does not support %d threads/core.",
> +                    smp_threads);
> +            kvmppc_hint_smt_possible(&local_err);
> +            goto out;
> +        }
> +    }

I'd like to see a fallback for kernels that don't support the
smt_possible cap and vsmt mode setting (for those, we must have
smp_threads <= kvm_smt).

> +
>      /* Detemine the VSMT mode to use: */
>      if (vsmt_user) {
>          if (spapr->vsmt < smp_threads) {
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index 914be687e7..4a8ff4d63c 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -2456,6 +2456,11 @@ bool kvmppc_has_cap_mmu_hash_v3(void)
>      return cap_mmu_hash_v3;
>  }
>  
> +int kvmppc_cap_smt_possible(void)
> +{
> +    return cap_ppc_smt_possible;
> +}
> +
>  PowerPCCPUClass *kvm_ppc_get_host_cpu_class(void)
>  {
>      uint32_t host_pvr = mfpvr();
> diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h
> index ecb55493cc..2221850723 100644
> --- a/target/ppc/kvm_ppc.h
> +++ b/target/ppc/kvm_ppc.h
> @@ -59,6 +59,7 @@ bool kvmppc_has_cap_fixup_hcalls(void);
>  bool kvmppc_has_cap_htm(void);
>  bool kvmppc_has_cap_mmu_radix(void);
>  bool kvmppc_has_cap_mmu_hash_v3(void);
> +int kvmppc_cap_smt_possible(void);
>  int kvmppc_enable_hwrng(void);
>  int kvmppc_put_books_sregs(PowerPCCPU *cpu);
>  PowerPCCPUClass *kvm_ppc_get_host_cpu_class(void);
> @@ -290,6 +291,11 @@ static inline bool kvmppc_has_cap_mmu_hash_v3(void)
>      return false;
>  }
>  
> +static inline int kvmppc_cap_smt_possible(void)
> +{
> +    return 0;
> +}
> +
>  static inline int kvmppc_enable_hwrng(void)
>  {
>      return -1;

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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