-----Original Message----- From: Schick, Stefan Sent: Thu 12/23/2010 12:52 PM To: Sowmya Sridharan Subject: RE: About runqueues in Linux -----Original Message----- From: kernelnewbies-bounces@kernelnewbies.org on behalf of Sowmya Sridharan Sent: Thu 12/23/2010 11:58 AM To: kernelnewbies@kernelnewbies.org Subject: About runqueues in Linux Greetings List, I have certain queries regarding the maintenance of runqueues in Linux. In case of an SMP system, will a same process be added to multiple runqueues? In the sample data given below, I am seeing that the process "Appstart" is added to the runqueue on CPU1, but it is not run on that CPU. Instead it is added to CPU0's runqueue, and it is run on that CPU. I have not affined the process to any CPU, and it is not multi-threaded. CPU1 data: Cpu: 1, HRT: 1290079896.698994, Pid: 6577, Pname: Appstart added_to_runqueue, current process: irc(6103) Cpu: 1, HRT: 1290079896.706994, Pid: 6103, Pname: irc added_to_runqueue,current process: swapper(0) CPU0 data: Cpu: 0, HRT: 1290079896.702994, Pid: 6577, Pname: Appstart added_to_runqueue, Current process: eventd(5370) Cpu: 0, HRT: 1290079896.702994, Pid: 14247, Pname: Conn_agent added_to_runqueue, Current process: Appstart(6577) What is the default CPU on which a process runs, if cpu affinity is not set? Is it possible that a process added to one runqueue can be moved to another runqueue? Also I have seen swapper getting scheduled frequently even if there are runnable processes. Shouldn't swapper be run, only if there are no runnable processes? Your insights will be appreciated. Regards, Sowmya =====-----=====-----===== Notice: The information contained in this e-mail message and/or attachments to it may contain confidential or privileged information. If you are not the intended recipient, any dissemination, use, review, distribution, printing or copying of the information contained in this e-mail message and/or attachments to it are strictly prohibited. If you have received this communication in error, please notify us by reply e-mail or telephone and immediately and permanently delete the message and any attachments. Thank you Hey Sowmya, one process can only be in one runqueue at the same time. What is the default CPU on which a process runs, if cpu affinity is not set? The CPU with the shortest runqueue. Is it possible that a process added to one runqueue can be moved to another runqueue? Yes, they can be pulled over, see load_balance() in sched_fair.c Also I have seen swapper getting scheduled frequently even if there are runnable processes. Shouldn't swapper be run, only if there are no runnable processes? No, because it is possible that a Process in the expired runqueue is starving. Regards Stefan