powerpc: Add virtual processor dispatch trace log

pseries SPLPAR machines are able to retrieve a log of dispatch and
preempt events from the hypervisor. With this information, we can
see when and why each dispatch & preempt is occuring.

This change adds a set of debugfs files allowing userspace to read this
dispatch log.

Based on initial patches from Nishanth Aravamudan <nacc@us.ibm.com>.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 274 insertions, 0 deletions

diff --git a/arch/powerpc/platforms/pseries/dtl.c b/arch/powerpc/platforms/pseries/dtl.c
new file mode 100644
index 000000000000..dc9b0f81e60f
--- /dev/null
+++ b/arch/powerpc/platforms/pseries/dtl.c
@@ -0,0 +1,274 @@
+/*
+ * Virtual Processor Dispatch Trace Log
+ *
+ * (C) Copyright IBM Corporation 2009
+ *
+ * Author: Jeremy Kerr <jk@ozlabs.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2, or (at your option)
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <linux/init.h>
+#include <linux/debugfs.h>
+#include <asm/smp.h>
+#include <asm/system.h>
+#include <asm/uaccess.h>
+
+#include "plpar_wrappers.h"
+
+/*
+ * Layout of entries in the hypervisor's DTL buffer. Although we don't
+ * actually access the internals of an entry (we only need to know the size),
+ * we might as well define it here for reference.
+ */
+struct dtl_entry {
+        u8      dispatch_reason;
+        u8      preempt_reason;
+        u16     processor_id;
+        u32     enqueue_to_dispatch_time;
+        u32     ready_to_enqueue_time;
+        u32     waiting_to_ready_time;
+        u64     timebase;
+        u64     fault_addr;
+        u64     srr0;
+        u64     srr1;
+};
+
+struct dtl {
+        struct dtl_entry        *buf;
+        struct dentry           *file;
+        int                     cpu;
+        int                     buf_entries;
+        u64                     last_idx;
+};
+static DEFINE_PER_CPU(struct dtl, dtl);
+
+/*
+ * Dispatch trace log event mask:
+ * 0x7: 0x1: voluntary virtual processor waits
+ *      0x2: time-slice preempts
+ *      0x4: virtual partition memory page faults
+ */
+static u8 dtl_event_mask = 0x7;
+
+
+/*
+ * Size of per-cpu log buffers. Default is just under 16 pages worth.
+ */
+static int dtl_buf_entries = (16 * 85);
+
+
+static int dtl_enable(struct dtl *dtl)
+{
+        unsigned long addr;
+        int ret, hwcpu;
+
+        /* only allow one reader */
+        if (dtl->buf)
+                return -EBUSY;
+
+        /* we need to store the original allocation size for use during read */
+        dtl->buf_entries = dtl_buf_entries;
+
+        dtl->buf = kmalloc_node(dtl->buf_entries * sizeof(struct dtl_entry),
+                        GFP_KERNEL, cpu_to_node(dtl->cpu));
+        if (!dtl->buf) {
+                printk(KERN_WARNING "%s: buffer alloc failed for cpu %d\n",
+                                __func__, dtl->cpu);
+                return -ENOMEM;
+        }
+
+        /* Register our dtl buffer with the hypervisor. The HV expects the
+         * buffer size to be passed in the second word of the buffer */
+        ((u32 *)dtl->buf)[1] = dtl->buf_entries * sizeof(struct dtl_entry);
+
+        hwcpu = get_hard_smp_processor_id(dtl->cpu);
+        addr = __pa(dtl->buf);
+        ret = register_dtl(hwcpu, addr);
+        if (ret) {
+                printk(KERN_WARNING "%s: DTL registration for cpu %d (hw %d) "
+                       "failed with %d\n", __func__, dtl->cpu, hwcpu, ret);
+                kfree(dtl->buf);
+                return -EIO;
+        }
+
+        /* set our initial buffer indices */
+        dtl->last_idx = lppaca[dtl->cpu].dtl_idx = 0;
+
+        /* enable event logging */
+        lppaca[dtl->cpu].dtl_enable_mask = dtl_event_mask;
+
+        return 0;
+}
+
+static void dtl_disable(struct dtl *dtl)
+{
+        int hwcpu = get_hard_smp_processor_id(dtl->cpu);
+
+        lppaca[dtl->cpu].dtl_enable_mask = 0x0;
+
+        unregister_dtl(hwcpu, __pa(dtl->buf));
+
+        kfree(dtl->buf);
+        dtl->buf = NULL;
+        dtl->buf_entries = 0;
+}
+
+/* file interface */
+
+static int dtl_file_open(struct inode *inode, struct file *filp)
+{
+        struct dtl *dtl = inode->i_private;
+        int rc;
+
+        rc = dtl_enable(dtl);
+        if (rc)
+                return rc;
+
+        filp->private_data = dtl;
+        return 0;
+}
+
+static int dtl_file_release(struct inode *inode, struct file *filp)
+{
+        struct dtl *dtl = inode->i_private;
+        dtl_disable(dtl);
+        return 0;
+}
+
+static ssize_t dtl_file_read(struct file *filp, char __user *buf, size_t len,
+                loff_t *pos)
+{
+        int rc, cur_idx, last_idx, n_read, n_req, read_size;
+        struct dtl *dtl;
+
+        if ((len % sizeof(struct dtl_entry)) != 0)
+                return -EINVAL;
+
+        dtl = filp->private_data;
+
+        /* requested number of entries to read */
+        n_req = len / sizeof(struct dtl_entry);
+
+        /* actual number of entries read */
+        n_read = 0;
+
+        cur_idx = lppaca[dtl->cpu].dtl_idx;
+        last_idx = dtl->last_idx;
+
+        if (cur_idx - last_idx > dtl->buf_entries) {
+                pr_debug("%s: hv buffer overflow for cpu %d, samples lost\n",
+                                __func__, dtl->cpu);
+        }
+
+        cur_idx  %= dtl->buf_entries;
+        last_idx %= dtl->buf_entries;
+
+        /* read the tail of the buffer if we've wrapped */
+        if (last_idx > cur_idx) {
+                read_size = min(n_req, dtl->buf_entries - last_idx);
+
+                rc = copy_to_user(buf, &dtl->buf[last_idx],
+                                read_size * sizeof(struct dtl_entry));
+                if (rc)
+                        return -EFAULT;
+
+                last_idx = 0;
+                n_req -= read_size;
+                n_read += read_size;
+                buf += read_size * sizeof(struct dtl_entry);
+        }
+
+        /* .. and now the head */
+        read_size = min(n_req, cur_idx - last_idx);
+        rc = copy_to_user(buf, &dtl->buf[last_idx],
+                        read_size * sizeof(struct dtl_entry));
+        if (rc)
+                return -EFAULT;
+
+        n_read += read_size;
+        dtl->last_idx += n_read;
+
+        return n_read * sizeof(struct dtl_entry);
+}
+
+static struct file_operations dtl_fops = {
+        .open           = dtl_file_open,
+        .release        = dtl_file_release,
+        .read           = dtl_file_read,
+        .llseek         = no_llseek,
+};
+
+static struct dentry *dtl_dir;
+
+static int dtl_setup_file(struct dtl *dtl)
+{
+        char name[10];
+
+        sprintf(name, "cpu-%d", dtl->cpu);
+
+        dtl->file = debugfs_create_file(name, 0400, dtl_dir, dtl, &dtl_fops);
+        if (!dtl->file)
+                return -ENOMEM;
+
+        return 0;
+}
+
+static int dtl_init(void)
+{
+        struct dentry *event_mask_file, *buf_entries_file;
+        int rc, i;
+
+        if (!firmware_has_feature(FW_FEATURE_SPLPAR))
+                return -ENODEV;
+
+        /* set up common debugfs structure */
+
+        rc = -ENOMEM;
+        dtl_dir = debugfs_create_dir("dtl", powerpc_debugfs_root);
+        if (!dtl_dir) {
+                printk(KERN_WARNING "%s: can't create dtl root dir\n",
+                                __func__);
+                goto err;
+        }
+
+        event_mask_file = debugfs_create_x8("dtl_event_mask", 0600,
+                                dtl_dir, &dtl_event_mask);
+        buf_entries_file = debugfs_create_u32("dtl_buf_entries", 0600,
+                                dtl_dir, &dtl_buf_entries);
+
+        if (!event_mask_file || !buf_entries_file) {
+                printk(KERN_WARNING "%s: can't create dtl files\n", __func__);
+                goto err_remove_dir;
+        }
+
+        /* set up the per-cpu log structures */
+        for_each_possible_cpu(i) {
+                struct dtl *dtl = &per_cpu(dtl, i);
+                dtl->cpu = i;
+
+                rc = dtl_setup_file(dtl);
+                if (rc)
+                        goto err_remove_dir;
+        }
+
+        return 0;
+
+err_remove_dir:
+        debugfs_remove_recursive(dtl_dir);
+err:
+        return rc;
+}
+arch_initcall(dtl_init);