This reads the timebase at various points in the real-mode guest
entry/exit code and uses that to accumulate total, minimum and
maximum time spent in those parts of the code. Currently these
times are accumulated per vcpu in 5 parts of the code:
* rm_entry - time taken from the start of kvmppc_hv_entry() until
just before entering the guest.
* rm_intr - time from when we take a hypervisor interrupt in the
guest until we either re-enter the guest or decide to exit to the
host. This includes time spent handling hcalls in real mode.
* rm_exit - time from when we decide to exit the guest until the
return from kvmppc_hv_entry().
* guest - time spend in the guest
* cede - time spent napping in real mode due to an H_CEDE hcall
while other threads in the same vcore are active.
These times are exposed in debugfs in a directory per vcpu that
contains a file called "timings". This file contains one line for
each of the 5 timings above, with the name followed by a colon and
4 numbers, which are the count (number of times the code has been
executed), the total time, the minimum time, and the maximum time,
all in nanoseconds.
The overhead of the extra code amounts to about 29ns for an hcall that
is handled in real mode (e.g. H_SET_DABR), or 25%, and about 43ns for
an hcall that is handled in the host kernel in virtual mode
(e.g. H_PROD), or 1.2%. Since production environments may not wish to
incur this overhead, the new code is conditional on a new config
symbol, CONFIG_KVM_BOOK3S_HV_EXIT_TIMING.
Signed-off-by: Paul Mackerras <pau...@samba.org>
---
arch/powerpc/include/asm/kvm_host.h | 21 +++++
arch/powerpc/include/asm/time.h | 3 +
arch/powerpc/kernel/asm-offsets.c | 13 +++
arch/powerpc/kernel/time.c | 6 ++
arch/powerpc/kvm/Kconfig | 14 +++
arch/powerpc/kvm/book3s_hv.c | 150 ++++++++++++++++++++++++++++++++
arch/powerpc/kvm/book3s_hv_rmhandlers.S | 129 ++++++++++++++++++++++++++-
7 files changed, 334 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/include/asm/kvm_host.h
b/arch/powerpc/include/asm/kvm_host.h
index f1d0bbc..d2068bb 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -369,6 +369,14 @@ struct kvmppc_slb {
u8 base_page_size; /* MMU_PAGE_xxx */
};
+/* Struct used to accumulate timing information in HV real mode code */
+struct kvmhv_tb_accumulator {
+ u64 seqcount; /* used to synchronize access, also count * 2 */
+ u64 tb_total; /* total time in timebase ticks */
+ u64 tb_min; /* min time */
+ u64 tb_max; /* max time */
+};
+
# ifdef CONFIG_PPC_FSL_BOOK3E
#define KVMPPC_BOOKE_IAC_NUM 2
#define KVMPPC_BOOKE_DAC_NUM 2
@@ -657,6 +665,19 @@ struct kvm_vcpu_arch {
u32 emul_inst;
#endif
+
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+ struct kvmhv_tb_accumulator *cur_activity; /* What we're timing */
+ u64 cur_tb_start; /* when it started */
+ struct kvmhv_tb_accumulator rm_entry; /* real-mode entry code */
+ struct kvmhv_tb_accumulator rm_intr; /* real-mode intr handling */
+ struct kvmhv_tb_accumulator rm_exit; /* real-mode exit code */
+ struct kvmhv_tb_accumulator guest_time; /* guest execution */
+ struct kvmhv_tb_accumulator cede_time; /* time napping inside guest */
+
+ struct dentry *debugfs_dir;
+ struct dentry *debugfs_timings;
+#endif /* CONFIG_KVM_BOOK3S_HV_EXIT_TIMING */
};
#define VCPU_FPR(vcpu, i) (vcpu)->arch.fp.fpr[i][TS_FPROFFSET]
diff --git a/arch/powerpc/include/asm/time.h b/arch/powerpc/include/asm/time.h
index 03cbada..10fc784 100644
--- a/arch/powerpc/include/asm/time.h
+++ b/arch/powerpc/include/asm/time.h
@@ -211,5 +211,8 @@ extern void secondary_cpu_time_init(void);
DECLARE_PER_CPU(u64, decrementers_next_tb);
+/* Convert timebase ticks to nanoseconds */
+unsigned long long tb_to_ns(unsigned long long tb_ticks);
+
#endif /* __KERNEL__ */
#endif /* __POWERPC_TIME_H */
diff --git a/arch/powerpc/kernel/asm-offsets.c
b/arch/powerpc/kernel/asm-offsets.c
index 4717859..3fea721 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -459,6 +459,19 @@ int main(void)
DEFINE(VCPU_SPRG2, offsetof(struct kvm_vcpu, arch.shregs.sprg2));
DEFINE(VCPU_SPRG3, offsetof(struct kvm_vcpu, arch.shregs.sprg3));
#endif
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+ DEFINE(VCPU_TB_RMENTRY, offsetof(struct kvm_vcpu, arch.rm_entry));
+ DEFINE(VCPU_TB_RMINTR, offsetof(struct kvm_vcpu, arch.rm_intr));
+ DEFINE(VCPU_TB_RMEXIT, offsetof(struct kvm_vcpu, arch.rm_exit));
+ DEFINE(VCPU_TB_GUEST, offsetof(struct kvm_vcpu, arch.guest_time));
+ DEFINE(VCPU_TB_CEDE, offsetof(struct kvm_vcpu, arch.cede_time));
+ DEFINE(VCPU_CUR_ACTIVITY, offsetof(struct kvm_vcpu, arch.cur_activity));
+ DEFINE(VCPU_ACTIVITY_START, offsetof(struct kvm_vcpu,
arch.cur_tb_start));
+ DEFINE(TAS_SEQCOUNT, offsetof(struct kvmhv_tb_accumulator, seqcount));
+ DEFINE(TAS_TOTAL, offsetof(struct kvmhv_tb_accumulator, tb_total));
+ DEFINE(TAS_MIN, offsetof(struct kvmhv_tb_accumulator, tb_min));
+ DEFINE(TAS_MAX, offsetof(struct kvmhv_tb_accumulator, tb_max));
+#endif
DEFINE(VCPU_SHARED_SPRG3, offsetof(struct kvm_vcpu_arch_shared, sprg3));
DEFINE(VCPU_SHARED_SPRG4, offsetof(struct kvm_vcpu_arch_shared, sprg4));
DEFINE(VCPU_SHARED_SPRG5, offsetof(struct kvm_vcpu_arch_shared, sprg5));
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 2d7b33f..56f4484 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -608,6 +608,12 @@ void arch_suspend_enable_irqs(void)
}
#endif
+unsigned long long tb_to_ns(unsigned long long ticks)
+{
+ return mulhdu(ticks, tb_to_ns_scale) << tb_to_ns_shift;
+}
+EXPORT_SYMBOL_GPL(tb_to_ns);
+
/*
* Scheduler clock - returns current time in nanosec units.
*
diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
index 11850f3..2963e4d 100644
--- a/arch/powerpc/kvm/Kconfig
+++ b/arch/powerpc/kvm/Kconfig
@@ -110,6 +110,20 @@ config KVM_BOOK3S_64_PR
processor, including emulating 32-bit processors on a 64-bit
host.
+config KVM_BOOK3S_HV_EXIT_TIMING
+ bool "Detailed timing for hypervisor real-mode code"
+ depends on KVM_BOOK3S_HV_POSSIBLE && DEBUG_FS
+ ---help---
+ Calculate time taken for each vcpu in the real-mode guest entry,
+ exit, and interrupt handling code, plus time spent in the guest
+ and in nap mode due to idle (cede) while other threads are still
+ in the guest. The total, minimum and maximum times in nanoseconds
+ together with the number of executions are reported in debugfs in
+ kvm/vm#/vcpu#/timings. The overhead is of the order of 30 - 40
+ ns per exit on POWER8.
+
+ If unsure, say N.
+
config KVM_BOOKE_HV
bool
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index cb54d90..c7b18ac 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1423,6 +1423,154 @@ static struct kvmppc_vcore *kvmppc_vcore_create(struct
kvm *kvm, int core)
return vcore;
}
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+static struct debugfs_timings_element {
+ const char *name;
+ size_t offset;
+} timings[] = {
+ {"rm_entry", offsetof(struct kvm_vcpu, arch.rm_entry)},
+ {"rm_intr", offsetof(struct kvm_vcpu, arch.rm_intr)},
+ {"rm_exit", offsetof(struct kvm_vcpu, arch.rm_exit)},
+ {"guest", offsetof(struct kvm_vcpu, arch.guest_time)},
+ {"cede", offsetof(struct kvm_vcpu, arch.cede_time)},
+};
+
+#define N_TIMINGS (sizeof(timings) / sizeof(timings[0]))
+
+struct debugfs_timings_state {
+ struct kvm_vcpu *vcpu;
+ unsigned int buflen;
+ char buf[N_TIMINGS * 100];
+};
+
+static int debugfs_timings_open(struct inode *inode, struct file *file)
+{
+ struct kvm_vcpu *vcpu = inode->i_private;
+ struct debugfs_timings_state *p;
+
+ p = kzalloc(sizeof(*p), GFP_KERNEL);
+ if (!p)
+ return -ENOMEM;
+
+ kvm_get_kvm(vcpu->kvm);
+ p->vcpu = vcpu;
+ file->private_data = p;
+
+ return nonseekable_open(inode, file);
+}
+
+static int debugfs_timings_release(struct inode *inode, struct file *file)
+{
+ struct debugfs_timings_state *p = file->private_data;
+
+ kvm_put_kvm(p->vcpu->kvm);
+ kfree(p);
+ return 0;
+}
+
+static ssize_t debugfs_timings_read(struct file *file, char __user *buf,
+ size_t len, loff_t *ppos)
+{
+ struct debugfs_timings_state *p = file->private_data;
+ struct kvm_vcpu *vcpu = p->vcpu;
+ char *s, *buf_end;
+ struct kvmhv_tb_accumulator tb;
+ u64 count;
+ loff_t pos;
+ ssize_t n;
+ int i, loops;
+ bool ok;
+
+ if (!p->buflen) {
+ s = p->buf;
+ buf_end = s + sizeof(p->buf);
+ for (i = 0; i < N_TIMINGS; ++i) {
+ struct kvmhv_tb_accumulator *acc;
+
+ acc = (struct kvmhv_tb_accumulator *)
+ ((unsigned long)vcpu + timings[i].offset);
+ ok = false;
+ for (loops = 0; loops < 1000; ++loops) {
+ count = acc->seqcount;
+ if (!(count & 1)) {
+ smp_rmb();
+ tb = *acc;
+ smp_rmb();
+ if (count == acc->seqcount) {
+ ok = true;
+ break;
+ }
+ }
+ udelay(1);
+ }
+ if (!ok)
+ snprintf(s, buf_end - s, "%s: stuck\n",
+ timings[i].name);
+ else
+ snprintf(s, buf_end - s,
+ "%s: %llu %llu %llu %llu\n",
+ timings[i].name, count / 2,
+ tb_to_ns(tb.tb_total),
+ tb_to_ns(tb.tb_min),
+ tb_to_ns(tb.tb_max));
+ s += strlen(s);
+ }
+ p->buflen = s - p->buf;
+ }
+
+ pos = *ppos;
+ if (pos >= p->buflen)
+ return 0;
+ if (len > p->buflen - pos)
+ len = p->buflen - pos;
+ n = copy_to_user(buf, p->buf + pos, len);
+ if (n) {
+ if (n == len)
+ return -EFAULT;
+ len -= n;
+ }
+ *ppos = pos + len;
+ return len;
+}
+
+static ssize_t debugfs_timings_write(struct file *file, const char __user *buf,
+ size_t len, loff_t *ppos)
+{
+ return -EACCES;
+}
+
+static const struct file_operations debugfs_timings_ops = {
+ .owner = THIS_MODULE,
+ .open = debugfs_timings_open,
+ .release = debugfs_timings_release,
+ .read = debugfs_timings_read,
+ .write = debugfs_timings_write,
+ .llseek = generic_file_llseek,
+};
+
+/* Create a debugfs directory for the vcpu */
+static void debugfs_vcpu_init(struct kvm_vcpu *vcpu, unsigned int id)
+{
+ char buf[16];
+ struct kvm *kvm = vcpu->kvm;
+
+ snprintf(buf, sizeof(buf), "vcpu%u", id);
+ if (IS_ERR_OR_NULL(kvm->arch.debugfs_dir))
+ return;
+ vcpu->arch.debugfs_dir = debugfs_create_dir(buf, kvm->arch.debugfs_dir);
+ if (IS_ERR_OR_NULL(vcpu->arch.debugfs_dir))
+ return;
+ vcpu->arch.debugfs_timings =
+ debugfs_create_file("timings", 0444, vcpu->arch.debugfs_dir,
+ vcpu, &debugfs_timings_ops);
+}
+
+#else /* CONFIG_KVM_BOOK3S_HV_EXIT_TIMING */
+static void debugfs_vcpu_init(struct kvm_vcpu *vcpu, unsigned int id)
+{
+}
+#endif /* CONFIG_KVM_BOOK3S_HV_EXIT_TIMING */
+
static struct kvm_vcpu *kvmppc_core_vcpu_create_hv(struct kvm *kvm,
unsigned int id)
{
@@ -1492,6 +1640,8 @@ static struct kvm_vcpu *kvmppc_core_vcpu_create_hv(struct
kvm *kvm,
vcpu->arch.cpu_type = KVM_CPU_3S_64;
kvmppc_sanity_check(vcpu);
+ debugfs_vcpu_init(vcpu, id);
+
return vcpu;
free_vcpu:
diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index e9c3cb5..ee6ba4c 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -225,7 +225,13 @@ kvm_novcpu_wakeup:
/* Got an IPI but other vcpus aren't yet exiting, must be a latecomer */
ld r4, HSTATE_KVM_VCPU(r13)
cmpdi r4, 0
- bne kvmppc_got_guest
+ beq kvmppc_primary_no_guest
+
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+ addi r3, r4, VCPU_TB_RMENTRY
+ bl kvmhv_start_timing
+#endif
+ b kvmppc_got_guest
kvm_novcpu_exit:
b hdec_soon
@@ -376,6 +382,14 @@ kvmppc_hv_entry:
li r6, KVM_GUEST_MODE_HOST_HV
stb r6, HSTATE_IN_GUEST(r13)
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+ /* Store initial timestamp */
+ cmpdi r4, 0
+ beq 1f
+ addi r3, r4, VCPU_TB_RMENTRY
+ bl kvmhv_start_timing
+1:
+#endif
/* Clear out SLB */
li r6,0
slbmte r6,r6
@@ -880,6 +894,12 @@ fast_guest_return:
li r9, KVM_GUEST_MODE_GUEST_HV
stb r9, HSTATE_IN_GUEST(r13)
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+ /* Accumulate timing */
+ addi r3, r4, VCPU_TB_GUEST
+ bl kvmhv_accumulate_time
+#endif
+
/* Enter guest */
BEGIN_FTR_SECTION
@@ -917,6 +937,23 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
hrfid
b .
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+secondary_too_late:
+ cmpdi r4, 0
+ beq 11f
+ addi r3, r4, VCPU_TB_RMEXIT
+ bl kvmhv_accumulate_time
+11: b kvmhv_switch_to_host
+
+hdec_soon:
+ ld r4, HSTATE_KVM_VCPU(r13)
+ cmpdi r4, 0
+ beq 12f
+ addi r3, r4, VCPU_TB_RMEXIT
+ bl kvmhv_accumulate_time
+12: b kvmhv_do_exit
+#endif
+
/******************************************************************************
* *
* Exit code *
@@ -1002,6 +1039,16 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
stw r12,VCPU_TRAP(r9)
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+ addi r3, r9, VCPU_TB_RMINTR
+ mr r4, r9
+ bl kvmhv_accumulate_time
+ ld r5, VCPU_GPR(R5)(r9)
+ ld r6, VCPU_GPR(R6)(r9)
+ ld r7, VCPU_GPR(R7)(r9)
+ ld r8, VCPU_GPR(R8)(r9)
+#endif
+
/* Save HEIR (HV emulation assist reg) in emul_inst
if this is an HEI (HV emulation interrupt, e40) */
li r3,KVM_INST_FETCH_FAILED
@@ -1072,6 +1119,11 @@ guest_exit_cont: /* r9 = vcpu, r12 = trap, r13 =
paca */
cmpwi r12, BOOK3S_INTERRUPT_MACHINE_CHECK
beq machine_check_realmode
mc_cont:
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+ addi r3, r9, VCPU_TB_RMEXIT
+ mr r4, r9
+ bl kvmhv_accumulate_time
+#endif
/* Save guest CTRL register, set runlatch to 1 */
6: mfspr r6,SPRN_CTRLF
@@ -1416,7 +1468,10 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
slbia
ptesync
-hdec_soon: /* r12 = trap, r13 = paca */
+#ifndef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+hdec_soon:
+#endif
+kvmhv_do_exit: /* r12 = trap, r13 = paca */
/*
* POWER7/POWER8 guest -> host partition switch code.
* We don't have to lock against tlbies but we do
@@ -1475,7 +1530,10 @@ hdec_soon: /* r12 = trap, r13 =
paca */
addi r6,r6,PACA_SIZE
bne 42b
+#ifndef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
secondary_too_late:
+#endif
+kvmhv_switch_to_host:
/* Secondary threads wait for primary to do partition switch */
43: ld r5,HSTATE_KVM_VCORE(r13)
ld r4,VCORE_KVM(r5) /* pointer to struct kvm */
@@ -1561,6 +1619,15 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
1: addi r8,r8,16
.endr
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+ /* Finish timing, if we have a vcpu */
+ ld r4, HSTATE_KVM_VCPU(r13)
+ cmpdi r4, 0
+ li r3, 0
+ beq 2f
+ bl kvmhv_accumulate_time
+2:
+#endif
/* Unset guest mode */
li r0, KVM_GUEST_MODE_NONE
stb r0, HSTATE_IN_GUEST(r13)
@@ -2068,6 +2135,12 @@ _GLOBAL(kvmppc_h_cede)
/* save FP state */
bl kvmppc_save_fp
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+ ld r4, HSTATE_KVM_VCPU(r13)
+ addi r3, r4, VCPU_TB_CEDE
+ bl kvmhv_accumulate_time
+#endif
+
/*
* Take a nap until a decrementer or external or doobell interrupt
* occurs, with PECE1, PECE0 and PECEDP set in LPCR. Also clear the
@@ -2108,6 +2181,11 @@ kvm_end_cede:
/* Woken by external or decrementer interrupt */
ld r1, HSTATE_HOST_R1(r13)
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+ addi r3, r4, VCPU_TB_RMINTR
+ bl kvmhv_accumulate_time
+#endif
+
/* load up FP state */
bl kvmppc_load_fp
@@ -2428,3 +2506,50 @@ kvmppc_fix_pmao:
mtspr SPRN_PMC6, r3
isync
blr
+
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+/*
+ * Start timing an activity
+ * r3 = pointer to time accumulation struct, r4 = vcpu
+ */
+kvmhv_start_timing:
+ mftb r5
+ std r3, VCPU_CUR_ACTIVITY(r4)
+ std r5, VCPU_ACTIVITY_START(r4)
+ blr
+
+/*
+ * Accumulate time to one activity and start another.
+ * r3 = pointer to new time accumulation struct, r4 = vcpu
+ */
+kvmhv_accumulate_time:
+ ld r5, VCPU_CUR_ACTIVITY(r4)
+ ld r6, VCPU_ACTIVITY_START(r4)
+ std r3, VCPU_CUR_ACTIVITY(r4)
+ mftb r7
+ std r7, VCPU_ACTIVITY_START(r4)
+ cmpdi r5, 0
+ beqlr
+ subf r3, r6, r7
+ ld r8, TAS_SEQCOUNT(r5)
+ cmpdi r8, 0
+ addi r8, r8, 1
+ std r8, TAS_SEQCOUNT(r5)
+ lwsync
+ ld r7, TAS_TOTAL(r5)
+ add r7, r7, r3
+ std r7, TAS_TOTAL(r5)
+ ld r6, TAS_MIN(r5)
+ ld r7, TAS_MAX(r5)
+ beq 3f
+ cmpd r3, r6
+ bge 1f
+3: std r3, TAS_MIN(r5)
+1: cmpd r3, r7
+ ble 2f
+ std r3, TAS_MAX(r5)
+2: lwsync
+ addi r8, r8, 1
+ std r8, TAS_SEQCOUNT(r5)
+ blr
+#endif
--
2.1.4
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