On 8/4/2011 9:40 AM, lina wrote: > On Thu, Aug 4, 2011 at 10:29 PM, Robert Baron > <[email protected]> wrote: >> have you tried adding an '&' to the tasks you think can be run in >> parallel (as in running them in the background (ie 'mycmd myargs &'))? > > Thanks, > > "&" is cool. > now is fully running, but, there is another thing slow it down, the > nice level is 19. why is it so high? are there some root's setting?
Nice levels can be deceiving to those who don't understand how kernel scheduling works. For example, it is possible, and happens all the time really, that a program with a nice level of 19 will fully consume 100% of a processor's time until the program completes. The only time nice comes into play is when scheduling contention exists. This only occurs when there are more ready-to-run processes/threads than available processor time slice slots. On an 8 processor desktop with the default 1000Hz scheduler you have 8,000 scheduling slices per second. So unless your system has 8,001 ready to run processes every second, that nice level 19 process will get all the CPU time it needs. Nice is a relic of early UNIX when businesses and universities would have dozens to hundreds of concurrent users on serial TTY terminals running programs on a shared single processor machine. Nice allowed administrators to provide "fair" access to all users, or to make sure a critical batch job got the cycles it needed, even with many users running their programs. On today's multi-core desktops, nice is literally irrelevant. This is actually the case for most business UNIX/Linux systems as well, as almost all of them have excess processor capacity for their actual workloads. -- Stan -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected] Archive: http://lists.debian.org/[email protected]
