[PATCH] csa accounting taskstats update

ChangeLog:
   Feedbacks from Andrew Morton:
   - define TS_COMM_LEN to 32
   - change acct_stimexpd field of task_struct to be of
     cputime_t, which is to be used to save the tsk->stime
     of last timer interrupt update.
   - a new Documentation/accounting/taskstats-struct.txt
     to describe fields of taskstats struct.

   Feedback from Balbir Singh:
   - keep the stime of a task to be zero when both stime
     and utime are zero as recoreded in task_struct.

   Misc:
   - convert accumulated RSS/VM from platform dependent
     pages-ticks to MBytes-usecs in the kernel

Cc: Shailabh Nagar <nagar@watson.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Jes Sorensen <jes@sgi.com>
Cc: Chris Sturtivant <csturtiv@sgi.com>
Cc: Tony Ernst <tee@sgi.com>
Cc: Guillaume Thouvenin <guillaume.thouvenin@bull.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

Documentation/accounting/taskstats-struct.txt

@@ -0,0 +1,161 @@
+The struct taskstats
+--------------------
+
+This document contains an explanation of the struct taskstats fields.
+
+There are three different groups of fields in the struct taskstats:
+
+1) Common and basic accounting fields
+    If CONFIG_TASKSTATS is set, the taskstats inteface is enabled and
+    the common fields and basic accounting fields are collected for
+    delivery at do_exit() of a task.
+2) Delay accounting fields
+    These fields are placed between
+    /* Delay accounting fields start */
+    and
+    /* Delay accounting fields end */
+    Their values are collected if CONFIG_TASK_DELAY_ACCT is set.
+3) Extended accounting fields
+    These fields are placed between
+    /* Extended accounting fields start */
+    and
+    /* Extended accounting fields end */
+    Their values are collected if CONFIG_TASK_XACCT is set.
+
+Future extension should add fields to the end of the taskstats struct, and
+should not change the relative position of each field within the struct.
+
+
+struct taskstats {
+
+1) Common and basic accounting fields:
+	/* The version number of this struct. This field is always set to
+	 * TAKSTATS_VERSION, which is defined in <linux/taskstats.h>.
+	 * Each time the struct is changed, the value should be incremented.
+	 */
+	__u16	version;
+
+  	/* The exit code of a task. */
+	__u32	ac_exitcode;		/* Exit status */
+
+  	/* The accounting flags of a task as defined in <linux/acct.h>
+	 * Defined values are AFORK, ASU, ACOMPAT, ACORE, and AXSIG.
+	 */
+	__u8	ac_flag;		/* Record flags */
+
+  	/* The value of task_nice() of a task. */
+	__u8	ac_nice;		/* task_nice */
+
+  	/* The name of the command that started this task. */
+	char	ac_comm[TS_COMM_LEN];	/* Command name */
+
+  	/* The scheduling discipline as set in task->policy field. */
+	__u8	ac_sched;		/* Scheduling discipline */
+
+	__u8	ac_pad[3];
+	__u32	ac_uid;			/* User ID */
+	__u32	ac_gid;			/* Group ID */
+	__u32	ac_pid;			/* Process ID */
+	__u32	ac_ppid;		/* Parent process ID */
+
+  	/* The time when a task begins, in [secs] since 1970. */
+	__u32	ac_btime;		/* Begin time [sec since 1970] */
+
+  	/* The elapsed time of a task, in [usec]. */
+	__u64	ac_etime;		/* Elapsed time [usec] */
+
+  	/* The user CPU time of a task, in [usec]. */
+	__u64	ac_utime;		/* User CPU time [usec] */
+
+  	/* The system CPU time of a task, in [usec]. */
+	__u64	ac_stime;		/* System CPU time [usec] */
+
+  	/* The minor page fault count of a task, as set in task->min_flt. */
+	__u64	ac_minflt;		/* Minor Page Fault Count */
+
+	/* The major page fault count of a task, as set in task->maj_flt. */
+	__u64	ac_majflt;		/* Major Page Fault Count */
+
+
+2) Delay accounting fields:
+	/* Delay accounting fields start
+	 *
+	 * All values, until the comment "Delay accounting fields end" are
+	 * available only if delay accounting is enabled, even though the last
+	 * few fields are not delays
+	 *
+	 * xxx_count is the number of delay values recorded
+	 * xxx_delay_total is the corresponding cumulative delay in nanoseconds
+	 *
+	 * xxx_delay_total wraps around to zero on overflow
+	 * xxx_count incremented regardless of overflow
+	 */
+
+	/* Delay waiting for cpu, while runnable
+	 * count, delay_total NOT updated atomically
+	 */
+	__u64	cpu_count;
+	__u64	cpu_delay_total;
+
+	/* Following four fields atomically updated using task->delays->lock */
+
+	/* Delay waiting for synchronous block I/O to complete
+	 * does not account for delays in I/O submission
+	 */
+	__u64	blkio_count;
+	__u64	blkio_delay_total;
+
+	/* Delay waiting for page fault I/O (swap in only) */
+	__u64	swapin_count;
+	__u64	swapin_delay_total;
+
+	/* cpu "wall-clock" running time
+	 * On some architectures, value will adjust for cpu time stolen
+	 * from the kernel in involuntary waits due to virtualization.
+	 * Value is cumulative, in nanoseconds, without a corresponding count
+	 * and wraps around to zero silently on overflow
+	 */
+	__u64	cpu_run_real_total;
+
+	/* cpu "virtual" running time
+	 * Uses time intervals seen by the kernel i.e. no adjustment
+	 * for kernel's involuntary waits due to virtualization.
+	 * Value is cumulative, in nanoseconds, without a corresponding count
+	 * and wraps around to zero silently on overflow
+	 */
+	__u64	cpu_run_virtual_total;
+	/* Delay accounting fields end */
+	/* version 1 ends here */
+
+
+3) Extended accounting fields
+	/* Extended accounting fields start */
+
+	/* Accumulated RSS usage in duration of a task, in MBytes-usecs.
+	 * The current rss usage is added to this counter every time
+	 * a tick is charged to a task's system time. So, at the end we
+	 * will have memory usage multiplied by system time. Thus an
+	 * average usage per system time unit can be calculated.
+	 */
+	__u64	coremem;		/* accumulated RSS usage in MB-usec */
+
+  	/* Accumulated virtual memory usage in duration of a task.
+	 * Same as acct_rss_mem1 above except that we keep track of VM usage.
+	 */
+	__u64	virtmem;		/* accumulated VM usage in MB-usec */
+
+  	/* High watermark of RSS usage in duration of a task, in KBytes. */
+	__u64	hiwater_rss;		/* High-watermark of RSS usage */
+
+  	/* High watermark of VM  usage in duration of a task, in KBytes. */
+	__u64	hiwater_vm;		/* High-water virtual memory usage */
+
+	/* The following four fields are I/O statistics of a task. */
+	__u64	read_char;		/* bytes read */
+	__u64	write_char;		/* bytes written */
+	__u64	read_syscalls;		/* read syscalls */
+	__u64	write_syscalls;		/* write syscalls */
+
+	/* Extended accounting fields end */
+
+}