On Fri, 16 Aug 2013 14:51:59 +0100, emani murali said:

Exactly, I would like to know how is runq computed from load average. Are there any system calls to get this value.

Load average is computed from runq. Not the other way around. Given runq, you can comput load average. Given load average, ti's very difficult to compute runq. Omeletts are made from eggs. Not the other way around. Given an egg, you can create an omelette. Given an omelette, it's very difficult to make an egg. The problem is that runq changes many times per second (potentially at every system call, and it doesn't take much hardware to do a quarter million system calls per second). Load average is a smoothed average value, and as such, loses information. If I tell you that the average amount of folding money in my wallet during July was $5.89, you can't figure out how much was in my wallet at 2PM on July 12, or if there was $8 more in it at 10AM that morning and I paid for lunch with cash that day. There's also the minor detail that the *average* inclues 89 cents - but folding money in the US is always an integer. :)

On Fri, 16 Aug 2013 12:57:23 -0400, Rik van Riel said:

On 08/16/2013 09:20 AM, emani murali wrote:

...

Hi,

I'm trying to obtain number of runnable processes from linux kernel. sar -q gives this information readily. However I'm trying to get this value from /proc filesystem. There is no file in /proc that gives this value directly, then how is runq-sz computed.

Tools like top, vmstat, and sar, simply look at all the processes in /proc, and count the number that are in runnable (R) state.

Which is why I asked what Emani is trying to do - scanning /proc is inherently racy, and the runq-sz value can change and/or be different than counting the number of runnable processes. A slight bit of jitter in the output of top probably doesn't matter. Feeding the number back into a scheduler loop or something like that may matter a lot...