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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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15
include/linux/user_events.h
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@@ -20,15 +20,6 @@
#define USER_EVENTS_SYSTEM "user_events"
#define USER_EVENTS_PREFIX "u:"
/* Bits 0-6 are for known probe types, Bit 7 is for unknown probes */
#define EVENT_BIT_FTRACE 0
#define EVENT_BIT_PERF 1
#define EVENT_BIT_OTHER 7
#define EVENT_STATUS_FTRACE (1 << EVENT_BIT_FTRACE)
#define EVENT_STATUS_PERF (1 << EVENT_BIT_PERF)
#define EVENT_STATUS_OTHER (1 << EVENT_BIT_OTHER)
/* Create dynamic location entry within a 32-bit value */
#define DYN_LOC(offset, size) ((size) << 16 | (offset))
@@ -45,12 +36,12 @@ struct user_reg {
/* Input: Pointer to string with event name, description and flags */
__u64 name_args;
/* Output: Byte index of the event within the status page */
__u32 status_index;
/* Output: Bitwise index of the event within the status page */
__u32 status_bit;
/* Output: Index of the event to use when writing data */
__u32 write_index;
};
} __attribute__((__packed__));
#define DIAG_IOC_MAGIC '*'