perf_counter: new output ABI - part 1
Impact: Rework the perfcounter output ABI
use sys_read() only for instant data and provide mmap() output for all
async overflow data.
The first mmap() determines the size of the output buffer. The mmap()
size must be a PAGE_SIZE multiple of 1+pages, where pages must be a
power of 2 or 0. Further mmap()s of the same fd must have the same
size. Once all maps are gone, you can again mmap() with a new size.
In case of 0 extra pages there is no data output and the first page
only contains meta data.
When there are data pages, a poll() event will be generated for each
full page of data. Furthermore, the output is circular. This means
that although 1 page is a valid configuration, its useless, since
we'll start overwriting it the instant we report a full page.
Future work will focus on the output format (currently maintained)
where we'll likey want each entry denoted by a header which includes a
type and length.
Further future work will allow to splice() the fd, also containing the
async overflow data -- splice() would be mutually exclusive with
mmap() of the data.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Orig-LKML-Reference: <20090323172417.470536358@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 40b324e..2b5e66d 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -152,6 +152,8 @@
__u32 lock; /* seqlock for synchronization */
__u32 index; /* hardware counter identifier */
__s64 offset; /* add to hardware counter value */
+
+ __u32 data_head; /* head in the data section */
};
#ifdef __KERNEL__
@@ -218,21 +220,6 @@
#endif
};
-/*
- * Hardcoded buffer length limit for now, for IRQ-fed events:
- */
-#define PERF_DATA_BUFLEN 2048
-
-/**
- * struct perf_data - performance counter IRQ data sampling ...
- */
-struct perf_data {
- int len;
- int rd_idx;
- int overrun;
- u8 data[PERF_DATA_BUFLEN];
-};
-
struct perf_counter;
/**
@@ -256,6 +243,14 @@
struct file;
+struct perf_mmap_data {
+ struct rcu_head rcu_head;
+ int nr_pages;
+ atomic_t head;
+ struct perf_counter_mmap_page *user_page;
+ void *data_pages[0];
+};
+
/**
* struct perf_counter - performance counter kernel representation:
*/
@@ -289,16 +284,15 @@
int oncpu;
int cpu;
- /* pointer to page shared with userspace via mmap */
- unsigned long user_page;
+ /* mmap bits */
+ struct mutex mmap_mutex;
+ atomic_t mmap_count;
+ struct perf_mmap_data *data;
- /* read() / irq related data */
+ /* poll related */
wait_queue_head_t waitq;
/* optional: for NMIs */
int wakeup_pending;
- struct perf_data *irqdata;
- struct perf_data *usrdata;
- struct perf_data data[2];
void (*destroy)(struct perf_counter *);
struct rcu_head rcu_head;