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tracing/user_events: Use bits vs bytes for enabled status page data

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User processes may require many events and when they do the cache
performance of a byte index status check is less ideal than a bit index.
The previous event limit per-page was 4096, the new limit is 32,768.

This change adds a bitwise index to the user_reg struct. Programs check
that the bit at status_bit has a bit set within the status page(s).

Link: https://lkml.kernel.org/r/20220728233309.1896-6-beaub@linux.microsoft.com
Link: https://lore.kernel.org/all/2059213643.196683.1648499088753.JavaMail.zimbra@efficios.com/

Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Beau Belgrave
2022-07-28 16:33:08 -07:00
committed by Steven Rostedt (Google)
parent d401b72458
commit 39d6d08b2e
5 changed files with 135 additions and 38 deletions
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75
kernel/trace/trace_events_user.c
View File

@@ -40,17 +40,44 @@
*/
#define MAX_PAGE_ORDER 0
#define MAX_PAGES (1 << MAX_PAGE_ORDER)
#define MAX_EVENTS (MAX_PAGES * PAGE_SIZE)
#define MAX_BYTES (MAX_PAGES * PAGE_SIZE)
#define MAX_EVENTS (MAX_BYTES * 8)
/* Limit how long of an event name plus args within the subsystem. */
#define MAX_EVENT_DESC 512
#define EVENT_NAME(user_event) ((user_event)->tracepoint.name)
#define MAX_FIELD_ARRAY_SIZE 1024
/*
* The MAP_STATUS_* macros are used for taking a index and determining the
* appropriate byte and the bit in the byte to set/reset for an event.
*
* The lower 3 bits of the index decide which bit to set.
* The remaining upper bits of the index decide which byte to use for the bit.
*
* This is used when an event has a probe attached/removed to reflect live
* status of the event wanting tracing or not to user-programs via shared
* memory maps.
*/
#define MAP_STATUS_BYTE(index) ((index) >> 3)
#define MAP_STATUS_MASK(index) BIT((index) & 7)
/*
* Internal bits (kernel side only) to keep track of connected probes:
* These are used when status is requested in text form about an event. These
* bits are compared against an internal byte on the event to determine which
* probes to print out to the user.
*
* These do not reflect the mapped bytes between the user and kernel space.
*/
#define EVENT_STATUS_FTRACE BIT(0)
#define EVENT_STATUS_PERF BIT(1)
#define EVENT_STATUS_OTHER BIT(7)
static char *register_page_data;
static DEFINE_MUTEX(reg_mutex);
static DEFINE_HASHTABLE(register_table, 4);
static DEFINE_HASHTABLE(register_table, 8);
static DECLARE_BITMAP(page_bitmap, MAX_EVENTS);
/*
@@ -72,6 +99,7 @@ struct user_event {
int index;
int flags;
int min_size;
char status;
};
/*
@@ -106,6 +134,22 @@ static u32 user_event_key(char *name)
return jhash(name, strlen(name), 0);
}
static __always_inline
void user_event_register_set(struct user_event *user)
{
int i = user->index;
register_page_data[MAP_STATUS_BYTE(i)] |= MAP_STATUS_MASK(i);
}
static __always_inline
void user_event_register_clear(struct user_event *user)
{
int i = user->index;
register_page_data[MAP_STATUS_BYTE(i)] &= ~MAP_STATUS_MASK(i);
}
static __always_inline __must_check
bool user_event_last_ref(struct user_event *user)
{
@@ -648,7 +692,7 @@ static int destroy_user_event(struct user_event *user)
dyn_event_remove(&user->devent);
register_page_data[user->index] = 0;
user_event_register_clear(user);
clear_bit(user->index, page_bitmap);
hash_del(&user->node);
@@ -827,7 +871,12 @@ static void update_reg_page_for(struct user_event *user)
rcu_read_unlock_sched();
}
register_page_data[user->index] = status;
if (status)
user_event_register_set(user);
else
user_event_register_clear(user);
user->status = status;
}
/*
@@ -1332,7 +1381,17 @@ static long user_reg_get(struct user_reg __user *ureg, struct user_reg *kreg)
if (size > PAGE_SIZE)
return -E2BIG;
return copy_struct_from_user(kreg, sizeof(*kreg), ureg, size);
if (size < offsetofend(struct user_reg, write_index))
return -EINVAL;
ret = copy_struct_from_user(kreg, sizeof(*kreg), ureg, size);
if (ret)
return ret;
kreg->size = size;
return 0;
}
/*
@@ -1376,7 +1435,7 @@ static long user_events_ioctl_reg(struct file *file, unsigned long uarg)
return ret;
put_user((u32)ret, &ureg->write_index);
put_user(user->index, &ureg->status_index);
put_user(user->index, &ureg->status_bit);
return 0;
}
@@ -1485,7 +1544,7 @@ static int user_status_mmap(struct file *file, struct vm_area_struct *vma)
{
unsigned long size = vma->vm_end - vma->vm_start;
if (size != MAX_EVENTS)
if (size != MAX_BYTES)
return -EINVAL;
return remap_pfn_range(vma, vma->vm_start,
@@ -1520,7 +1579,7 @@ static int user_seq_show(struct seq_file *m, void *p)
mutex_lock(&reg_mutex);
hash_for_each(register_table, i, user, node) {
status = register_page_data[user->index];
status = user->status;
flags = user->flags;
seq_printf(m, "%d:%s", user->index, EVENT_NAME(user));