armbian/linux
0
0
Fork 0
mirror of https://github.com/armbian/linux.git synced 2026-01-06 10:13:00 -08:00
Code Issues Packages Projects Releases Wiki Activity

[PATCH] per task delay accounting taskstats interface: documentation fix

Browse Source 
Change documentation and example program to reflect the flow control issues
being addressed by the cpumask changes.

Signed-off-by: Shailabh Nagar <nagar@watson.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Shailabh Nagar
2006-07-14 00:24:45 -07:00
committed by Linus Torvalds
parent ad4ecbcba7
commit 9e06d3f9f6
2 changed files with 361 additions and 301 deletions
Download Patch File Download Diff File Expand all files Collapse all files

598
Documentation/accounting/getdelays.c
View File

File diff suppressed because it is too large Load Diff

64
Documentation/accounting/taskstats.txt
View File

@@ -26,20 +26,28 @@ leader - a process is deemed alive as long as it has any task belonging to it.
Usage
-----
To get statistics during task's lifetime, userspace opens a unicast netlink
To get statistics during a task's lifetime, userspace opens a unicast netlink
socket (NETLINK_GENERIC family) and sends commands specifying a pid or a tgid.
The response contains statistics for a task (if pid is specified) or the sum of
statistics for all tasks of the process (if tgid is specified).
To obtain statistics for tasks which are exiting, userspace opens a multicast
netlink socket. Each time a task exits, its per-pid statistics is always sent
by the kernel to each listener on the multicast socket. In addition, if it is
the last thread exiting its thread group, an additional record containing the
per-tgid stats are also sent. The latter contains the sum of per-pid stats for
all threads in the thread group, both past and present.
To obtain statistics for tasks which are exiting, the userspace listener
sends a register command and specifies a cpumask. Whenever a task exits on
one of the cpus in the cpumask, its per-pid statistics are sent to the
registered listener. Using cpumasks allows the data received by one listener
to be limited and assists in flow control over the netlink interface and is
explained in more detail below.
If the exiting task is the last thread exiting its thread group,
an additional record containing the per-tgid stats is also sent to userspace.
The latter contains the sum of per-pid stats for all threads in the thread
group, both past and present.
getdelays.c is a simple utility demonstrating usage of the taskstats interface
for reporting delay accounting statistics.
for reporting delay accounting statistics. Users can register cpumasks,
send commands and process responses, listen for per-tid/tgid exit data,
write the data received to a file and do basic flow control by increasing
receive buffer sizes.
Interface
---------
@@ -66,10 +74,20 @@ The messages are in the format
The taskstats payload is one of the following three kinds:
1. Commands: Sent from user to kernel. The payload is one attribute, of type
TASKSTATS_CMD_ATTR_PID/TGID, containing a u32 pid or tgid in the attribute
payload. The pid/tgid denotes the task/process for which userspace wants
statistics.
1. Commands: Sent from user to kernel. Commands to get data on
a pid/tgid consist of one attribute, of type TASKSTATS_CMD_ATTR_PID/TGID,
containing a u32 pid or tgid in the attribute payload. The pid/tgid denotes
the task/process for which userspace wants statistics.
Commands to register/deregister interest in exit data from a set of cpus
consist of one attribute, of type
TASKSTATS_CMD_ATTR_REGISTER/DEREGISTER_CPUMASK and contain a cpumask in the
attribute payload. The cpumask is specified as an ascii string of
comma-separated cpu ranges e.g. to listen to exit data from cpus 1,2,3,5,7,8
the cpumask would be "1-3,5,7-8". If userspace forgets to deregister interest
in cpus before closing the listening socket, the kernel cleans up its interest
set over time. However, for the sake of efficiency, an explicit deregistration
is advisable.
2. Response for a command: sent from the kernel in response to a userspace
command. The payload is a series of three attributes of type:
@@ -138,4 +156,26 @@ struct too much, requiring disparate userspace accounting utilities to
unnecessarily receive large structures whose fields are of no interest, then
extending the attributes structure would be worthwhile.
Flow control for taskstats
--------------------------
When the rate of task exits becomes large, a listener may not be able to keep
up with the kernel's rate of sending per-tid/tgid exit data leading to data
loss. This possibility gets compounded when the taskstats structure gets
extended and the number of cpus grows large.
To avoid losing statistics, userspace should do one or more of the following:
- increase the receive buffer sizes for the netlink sockets opened by
listeners to receive exit data.
- create more listeners and reduce the number of cpus being listened to by
each listener. In the extreme case, there could be one listener for each cpu.
Users may also consider setting the cpu affinity of the listener to the subset
of cpus to which it listens, especially if they are listening to just one cpu.
Despite these measures, if the userspace receives ENOBUFS error messages
indicated overflow of receive buffers, it should take measures to handle the
loss of data.
----