KVM: PPC: Book3S HV: Accumulate timing information for real-mode code

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 30ns for an hcall that
is handled in real mode (e.g. H_SET_DABR), which is about 25%.  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 <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

1 files changed, 150 insertions, 0 deletions

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 08f8617f4046..64a02d4c737c 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: