Kbase 17188: Unix Process priorities and How Progress Uses Them
| Autor |
Progress Software Corporation - Progress |
| Acesso |
Público |
| Publicação |
10/05/1998 |
|
Unix Process priorities and How Progress Uses Them
This knowledgebase is to provide insight into what the process
priority is, how Progress tends to use them, and the possible dangers
of interfering with the UNIX delegation of them. The process priority
is the fourth field from the left of a ps -ef listing grepped for a
particular user. For example:
ps -ef|grep damore
damore 27715 27714 0 09:39:42 ttyp6 0:00 -sh
damore 27732 27731 6 09:40:01 ttyp6 0:00 ps -ef
damore 27696 27695 0 09:26:08 ttyp1 0:00 -sh
damore 27731 27715 1 09:40:01 ttyp6 0:00 grep damore
damore 26877 1 0 Aug 14 ? 0:00 /usr1/73D01/dlc/bin/_mp
rosrv rob
In this example, the fiourth field is the process priority number.
Here you can see that the ps
process and the grep process get high priority numbers, which results
in less process time from the cpu. The _mprosrv has a very low
priority number which results in more processing time by the cpu.
Progress typically reserves these low priority numbers for high
priority processes, and root typically recieves 0 or 1 as priority.
Typical user processes, such as damore in the example, tend to get
higher priority numbers resulting in less cpu time. This can be
changed with the UNIX nice command, which is defined in the man page
as invoking a command with an altered scheduling priority. It is NOT
recommended or supported to use nice for changing Progress process
priorities and here is why.
If a user has "niced" their process priority, there can be instances
where a contention situation can be created, and the consequences can
result in a significant performance hit, among other things. For
example, a user logs in with a "niced" user priority and recieves a
very low process priority number. The user then acquires a latch in
shared memory. Because this user now has a low priority number, thus
more cpu time, they are more likely to get swapped out as to avoid
"hogging" of the cpu. Meanwhile, an important Progress process such as
an APW is waiting on that same latch but can't acquire it because the
user holding it has been swapped out. This means that two processes
are in contention for the same latch, and in this case a waiting APW
means instant i/o and performance degradation. Latch contention was
a particular problem in earlier versions of 6, and this kind of
situation can only make things worse.
Basically, Progress reserves the lower priority numbers and higher
cpu time for more important processes and utilities. This is by design
and should NEVER be manipulated, especially when using the UNIX nice
command. For more information on nice or the process priority number,
consult your operating system documentation or the the operating
system man page on each.
sda 8/20/97
Progress Software Technical Support Note # 17188