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>

1 files changed, 15 insertions, 21 deletions

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 40b324e91bf6..2b5e66d5ebdf 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -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;