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perf_counter: new output ABI - part 1

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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>
This commit is contained in:
Peter Zijlstra
2009-03-23 18:22:10 +01:00
committed by Ingo Molnar
parent b09d2501ed
commit 7b732a7504
3 changed files with 263 additions and 246 deletions
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36
include/linux/perf_counter.h
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@ -152,6 +152,8 @@ struct perf_counter_mmap_page {
__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 @@ struct hw_perf_counter {
#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 @@ enum perf_counter_active_state {
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 @@ struct perf_counter {
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;