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ANDROID: ring-buffer: Expose buffer_data_page material

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In preparation for allowing the write of ring-buffer compliant pages
outside of ring_buffer.c move to the header, struct buffer_data_page and
timestamp encoding functions.

When I presented this work to the tracingsummit, rosted@ told me he saw
some overlapping with an idea he had to enable him to map the tracing
buffers in userspace. We designed together a solution that would enable
both features. Problem now, if on one hand, the development of the new
design has started already... it would nonetheless impose a significant
revamp of this patchset, which wouldn't make it to Android14. Nothing
technically wrong with anything here, but sending it to LKML wouldn't
make sense, as I know already this isn't as "reusable" as the version
agreed upon.

Bug: 229972309
Change-Id: Icf3329bd899a3dd91279d1bbadaf2dc4e243455c
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
This commit is contained in:
Vincent Donnefort
2022-08-24 13:31:24 +01:00
parent 2d1a2452a6
commit 54c734c8ed
2 changed files with 44 additions and 41 deletions
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44
include/linux/ring_buffer.h
View File

@@ -3,8 +3,10 @@
#define _LINUX_RING_BUFFER_H
#include <linux/mm.h>
#include <linux/seq_file.h>
#include <linux/poll.h>
#include <linux/seq_file.h>
#include <asm/local.h>
struct trace_buffer;
struct ring_buffer_iter;
@@ -18,6 +20,8 @@ struct ring_buffer_event {
u32 array[];
};
#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
/**
* enum ring_buffer_type - internal ring buffer types
*
@@ -59,11 +63,49 @@ enum ring_buffer_type {
RINGBUF_TYPE_TIME_STAMP,
};
#define TS_SHIFT 27
#define TS_MASK ((1ULL << TS_SHIFT) - 1)
#define TS_DELTA_TEST (~TS_MASK)
/*
* We need to fit the time_stamp delta into 27 bits.
*/
static inline int test_time_stamp(u64 delta)
{
if (delta & TS_DELTA_TEST)
return 1;
return 0;
}
unsigned ring_buffer_event_length(struct ring_buffer_event *event);
void *ring_buffer_event_data(struct ring_buffer_event *event);
u64 ring_buffer_event_time_stamp(struct trace_buffer *buffer,
struct ring_buffer_event *event);
#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)
#define BUF_PAGE_SIZE (PAGE_SIZE - BUF_PAGE_HDR_SIZE)
#define RB_ALIGNMENT 4U
#define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
#define RB_EVNT_MIN_SIZE 8U /* two 32bit words */
#ifndef CONFIG_HAVE_64BIT_ALIGNED_ACCESS
# define RB_FORCE_8BYTE_ALIGNMENT 0
# define RB_ARCH_ALIGNMENT RB_ALIGNMENT
#else
# define RB_FORCE_8BYTE_ALIGNMENT 1
# define RB_ARCH_ALIGNMENT 8U
#endif
#define RB_ALIGN_DATA __aligned(RB_ARCH_ALIGNMENT)
struct buffer_data_page {
u64 time_stamp; /* page time stamp */
local_t commit; /* write committed index */
unsigned char data[] RB_ALIGN_DATA; /* data of buffer page */
};
/*
* ring_buffer_discard_commit will remove an event that has not
* been committed yet. If this is used, then ring_buffer_unlock_commit

41
kernel/trace/ring_buffer.c
View File

@@ -132,23 +132,6 @@ int ring_buffer_print_entry_header(struct trace_seq *s)
/* Used for individual buffers (after the counter) */
#define RB_BUFFER_OFF (1 << 20)
#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)
#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
#define RB_ALIGNMENT 4U
#define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
#define RB_EVNT_MIN_SIZE 8U /* two 32bit words */
#ifndef CONFIG_HAVE_64BIT_ALIGNED_ACCESS
# define RB_FORCE_8BYTE_ALIGNMENT 0
# define RB_ARCH_ALIGNMENT RB_ALIGNMENT
#else
# define RB_FORCE_8BYTE_ALIGNMENT 1
# define RB_ARCH_ALIGNMENT 8U
#endif
#define RB_ALIGN_DATA __aligned(RB_ARCH_ALIGNMENT)
/* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
#define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
@@ -291,10 +274,6 @@ EXPORT_SYMBOL_GPL(ring_buffer_event_data);
#define for_each_online_buffer_cpu(buffer, cpu) \
for_each_cpu_and(cpu, buffer->cpumask, cpu_online_mask)
#define TS_SHIFT 27
#define TS_MASK ((1ULL << TS_SHIFT) - 1)
#define TS_DELTA_TEST (~TS_MASK)
static u64 rb_event_time_stamp(struct ring_buffer_event *event)
{
u64 ts;
@@ -311,12 +290,6 @@ static u64 rb_event_time_stamp(struct ring_buffer_event *event)
/* Missed count stored at end */
#define RB_MISSED_STORED (1 << 30)
struct buffer_data_page {
u64 time_stamp; /* page time stamp */
local_t commit; /* write committed index */
unsigned char data[] RB_ALIGN_DATA; /* data of buffer page */
};
/*
* Note, the buffer_page list must be first. The buffer pages
* are allocated in cache lines, which means that each buffer
@@ -364,18 +337,6 @@ static void free_buffer_page(struct buffer_page *bpage)
kfree(bpage);
}
/*
* We need to fit the time_stamp delta into 27 bits.
*/
static inline int test_time_stamp(u64 delta)
{
if (delta & TS_DELTA_TEST)
return 1;
return 0;
}
#define BUF_PAGE_SIZE (PAGE_SIZE - BUF_PAGE_HDR_SIZE)
/* Max payload is BUF_PAGE_SIZE - header (8bytes) */
#define BUF_MAX_DATA_SIZE (BUF_PAGE_SIZE - (sizeof(u32) * 2))
@@ -3488,7 +3449,7 @@ static void check_buffer(struct ring_buffer_per_cpu *cpu_buffer,
return;
/*
* If this interrupted another event,
* If this interrupted another event,
*/
if (atomic_inc_return(this_cpu_ptr(&checking)) != 1)
goto out;