--- /dev/null
+Version 15 of schedstats dropped counters for some sched_yield:
+yld_exp_empty, yld_act_empty and yld_both_empty. Otherwise, it is
+identical to version 14.
+
+Version 14 of schedstats includes support for sched_domains, which hit the
+mainline kernel in 2.6.20 although it is identical to the stats from version
+12 which was in the kernel from 2.6.13-2.6.19 (version 13 never saw a kernel
+release). Some counters make more sense to be per-runqueue; other to be
+per-domain. Note that domains (and their associated information) will only
+be pertinent and available on machines utilizing CONFIG_SMP.
+
+In version 14 of schedstat, there is at least one level of domain
+statistics for each cpu listed, and there may well be more than one
+domain. Domains have no particular names in this implementation, but
+the highest numbered one typically arbitrates balancing across all the
+cpus on the machine, while domain0 is the most tightly focused domain,
+sometimes balancing only between pairs of cpus. At this time, there
+are no architectures which need more than three domain levels. The first
+field in the domain stats is a bit map indicating which cpus are affected
+by that domain.
+
+These fields are counters, and only increment. Programs which make use
+of these will need to start with a baseline observation and then calculate
+the change in the counters at each subsequent observation. A perl script
+which does this for many of the fields is available at
+
+ http://eaglet.rain.com/rick/linux/schedstat/
+
+Note that any such script will necessarily be version-specific, as the main
+reason to change versions is changes in the output format. For those wishing
+to write their own scripts, the fields are described here.
+
+CPU statistics
+--------------
+cpu<N> 1 2 3 4 5 6 7 8 9
+
+First field is a sched_yield() statistic:
+ 1) # of times sched_yield() was called
+
+Next three are schedule() statistics:
+ 2) This field is a legacy array expiration count field used in the O(1)
+ scheduler. We kept it for ABI compatibility, but it is always set to zero.
+ 3) # of times schedule() was called
+ 4) # of times schedule() left the processor idle
+
+Next two are try_to_wake_up() statistics:
+ 5) # of times try_to_wake_up() was called
+ 6) # of times try_to_wake_up() was called to wake up the local cpu
+
+Next three are statistics describing scheduling latency:
+ 7) sum of all time spent running by tasks on this processor (in jiffies)
+ 8) sum of all time spent waiting to run by tasks on this processor (in
+ jiffies)
+ 9) # of timeslices run on this cpu
+
+
+Domain statistics
+-----------------
+One of these is produced per domain for each cpu described. (Note that if
+CONFIG_SMP is not defined, *no* domains are utilized and these lines
+will not appear in the output.)
+
+domain<N> <cpumask> 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
+
+The first field is a bit mask indicating what cpus this domain operates over.
+
+The next 24 are a variety of load_balance() statistics in grouped into types
+of idleness (idle, busy, and newly idle):
+
+ 1) # of times in this domain load_balance() was called when the
+ cpu was idle
+ 2) # of times in this domain load_balance() checked but found
+ the load did not require balancing when the cpu was idle
+ 3) # of times in this domain load_balance() tried to move one or
+ more tasks and failed, when the cpu was idle
+ 4) sum of imbalances discovered (if any) with each call to
+ load_balance() in this domain when the cpu was idle
+ 5) # of times in this domain pull_task() was called when the cpu
+ was idle
+ 6) # of times in this domain pull_task() was called even though
+ the target task was cache-hot when idle
+ 7) # of times in this domain load_balance() was called but did
+ not find a busier queue while the cpu was idle
+ 8) # of times in this domain a busier queue was found while the
+ cpu was idle but no busier group was found
+
+ 9) # of times in this domain load_balance() was called when the
+ cpu was busy
+ 10) # of times in this domain load_balance() checked but found the
+ load did not require balancing when busy
+ 11) # of times in this domain load_balance() tried to move one or
+ more tasks and failed, when the cpu was busy
+ 12) sum of imbalances discovered (if any) with each call to
+ load_balance() in this domain when the cpu was busy
+ 13) # of times in this domain pull_task() was called when busy
+ 14) # of times in this domain pull_task() was called even though the
+ target task was cache-hot when busy
+ 15) # of times in this domain load_balance() was called but did not
+ find a busier queue while the cpu was busy
+ 16) # of times in this domain a busier queue was found while the cpu
+ was busy but no busier group was found
+
+ 17) # of times in this domain load_balance() was called when the
+ cpu was just becoming idle
+ 18) # of times in this domain load_balance() checked but found the
+ load did not require balancing when the cpu was just becoming idle
+ 19) # of times in this domain load_balance() tried to move one or more
+ tasks and failed, when the cpu was just becoming idle
+ 20) sum of imbalances discovered (if any) with each call to
+ load_balance() in this domain when the cpu was just becoming idle
+ 21) # of times in this domain pull_task() was called when newly idle
+ 22) # of times in this domain pull_task() was called even though the
+ target task was cache-hot when just becoming idle
+ 23) # of times in this domain load_balance() was called but did not
+ find a busier queue while the cpu was just becoming idle
+ 24) # of times in this domain a busier queue was found while the cpu
+ was just becoming idle but no busier group was found
+
+ Next three are active_load_balance() statistics:
+ 25) # of times active_load_balance() was called
+ 26) # of times active_load_balance() tried to move a task and failed
+ 27) # of times active_load_balance() successfully moved a task
+
+ Next three are sched_balance_exec() statistics:
+ 28) sbe_cnt is not used
+ 29) sbe_balanced is not used
+ 30) sbe_pushed is not used
+
+ Next three are sched_balance_fork() statistics:
+ 31) sbf_cnt is not used
+ 32) sbf_balanced is not used
+ 33) sbf_pushed is not used
+
+ Next three are try_to_wake_up() statistics:
+ 34) # of times in this domain try_to_wake_up() awoke a task that
+ last ran on a different cpu in this domain
+ 35) # of times in this domain try_to_wake_up() moved a task to the
+ waking cpu because it was cache-cold on its own cpu anyway
+ 36) # of times in this domain try_to_wake_up() started passive balancing
+
+/proc/<pid>/schedstat
+----------------
+schedstats also adds a new /proc/<pid>/schedstat file to include some of
+the same information on a per-process level. There are three fields in
+this file correlating for that process to:
+ 1) time spent on the cpu
+ 2) time spent waiting on a runqueue
+ 3) # of timeslices run on this cpu
+
+A program could be easily written to make use of these extra fields to
+report on how well a particular process or set of processes is faring
+under the scheduler's policies. A simple version of such a program is
+available at
+ http://eaglet.rain.com/rick/linux/schedstat/v12/latency.c
Code Review / kvmfornfv.git / blobdiff