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Add visibility in to arc_read

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This change is an attempt to add visibility into the arc_read calls
occurring on a system, in real time. To do this, a list was added to the
in memory SPA data structure for a pool, with each element on the list
corresponding to a call to arc_read. These entries are then exported
through the kstat interface, which can then be interpreted in userspace.

For each arc_read call, the following information is exported:

 * A unique identifier (uint64_t)
 * The time the entry was added to the list (hrtime_t)
   (*not* wall clock time; relative to the other entries on the list)
 * The objset ID (uint64_t)
 * The object number (uint64_t)
 * The indirection level (uint64_t)
 * The block ID (uint64_t)
 * The name of the function originating the arc_read call (char[24])
 * The arc_flags from the arc_read call (uint32_t)
 * The PID of the reading thread (pid_t)
 * The command or name of thread originating read (char[16])

From this exported information one can see, in real time, exactly what
is being read, what function is generating the read, and whether or not
the read was found to be already cached.

There is still some work to be done, but this should serve as a good
starting point.

Specifically, dbuf_read's are not accounted for in the currently
exported information. Thus, a follow up patch should probably be added
to export these calls that never call into arc_read (they only hit the
dbuf hash table). In addition, it might be nice to create a utility
similar to "arcstat.py" to digest the exported information and display
it in a more readable format. Or perhaps, log the information and allow
for it to be "replayed" at a later time.

Signed-off-by: Prakash Surya <surya1@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
This commit is contained in:
Prakash Surya
2013-09-06 16:09:05 -07:00
committed by Brian Behlendorf
parent 76463d4026
commit 1421c89142
11 changed files with 310 additions and 13 deletions
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include/sys/spa.h
+21
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@@ -51,6 +51,8 @@ typedef struct zilog zilog_t;
typedef struct spa_aux_vdev spa_aux_vdev_t;
typedef struct ddt ddt_t;
typedef struct ddt_entry ddt_entry_t;
typedef struct zbookmark zbookmark_t;
struct dsl_pool;
struct dsl_dataset;
@@ -534,6 +536,25 @@ extern boolean_t spa_refcount_zero(spa_t *spa);
#define SCL_ALL ((1 << SCL_LOCKS) - 1)
#define SCL_STATE_ALL (SCL_STATE | SCL_L2ARC | SCL_ZIO)
/* Historical pool statistics */
typedef struct spa_stats_history {
kmutex_t lock;
uint64_t count;
uint64_t size;
kstat_t *kstat;
void *private;
list_t list;
} spa_stats_history_t;
typedef struct spa_stats {
spa_stats_history_t read_history;
} spa_stats_t;
extern void spa_stats_init(spa_t *spa);
extern void spa_stats_destroy(spa_t *spa);
extern void spa_read_history_add(spa_t *spa, const zbookmark_t *zb,
uint32_t aflags);
/* Pool configuration locks */
extern int spa_config_tryenter(spa_t *spa, int locks, void *tag, krw_t rw);
extern void spa_config_enter(spa_t *spa, int locks, void *tag, krw_t rw);