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Question about WCHAN values
Post 303044500 by bodisha on Monday 24th of February 2020 11:08:24 AM
02-24-2020
Question about WCHAN values
I have a CentOS 8 (3.10) running on VirtualBox 6.0... And I have 2 questions about WCHAN
The 'ps' man page describes WCHAN as:
I haven't see the "*" yet, but I'll see a "?" in the output of the "ps" command with regularity. Usually associated with the rcu_sched kernel process, but the "?" does appear for other processes. I haven't found a definition for the "?"... What does it mean?
My 2nd question is about a discrepancy I'm seeing between the output of the 'ps' command and the 'System Monitor' GUI utility. Under the 'ps' command, I'll see several processes in a run state and will have a "-" under WCHAN. Yet under the "System Monitor", those same processes will be in a run state with a WCHAN code of "poll_schedule_timeout". From what I've read this indicates a process is waiting for I/O... Shouldn't these processes be in a sleep state?
The 'ps' man page describes WCHAN as:
Quote:
nwchan WCHAN address of the kernel function where the process
is sleeping (use wchan if you want the kernel
function name). Running tasks will display a
dash ('-') in this column.
wchan WCHAN name of the kernel function in which the process
is sleeping, a "-" if the process is running, or
a "*" if the process is multi-threaded and ps is
not displaying threads.
is sleeping (use wchan if you want the kernel
function name). Running tasks will display a
dash ('-') in this column.
wchan WCHAN name of the kernel function in which the process
is sleeping, a "-" if the process is running, or
a "*" if the process is multi-threaded and ps is
not displaying threads.
I haven't see the "*" yet, but I'll see a "?" in the output of the "ps" command with regularity. Usually associated with the rcu_sched kernel process, but the "?" does appear for other processes. I haven't found a definition for the "?"... What does it mean?
My 2nd question is about a discrepancy I'm seeing between the output of the 'ps' command and the 'System Monitor' GUI utility. Under the 'ps' command, I'll see several processes in a run state and will have a "-" under WCHAN. Yet under the "System Monitor", those same processes will be in a run state with a WCHAN code of "poll_schedule_timeout". From what I've read this indicates a process is waiting for I/O... Shouldn't these processes be in a sleep state?
Last edited by bodisha; 02-24-2020 at 01:45 PM..
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LEARN ABOUT OSF1
sleep
sleep(9r) sleep(9r) NAME
sleep - General: Puts a calling process to sleep SYNOPSIS
void sleep( caddr_t *channel, long pri ); ARGUMENTS
Specifies a unique address associated with the calling kernel thread to be put to sleep. Specifies whether the sleep request is interrupt- ible. Setting this argument to the PCATCH flag causes the process to sleep in an interruptible state (that is, the kernel thread can take asynchronous signals). Not setting the PCATCH flag causes the process to sleep in an uninterruptible state (that is, the kernel thread can- not take asynchronous signals). DESCRIPTION
The sleep routine puts a calling process to sleep on the address specified by the channel argument. Some common addresses are the lbolt argument, a buf structure, and a proc structure. This address should be unique to prevent unexpected wake/sleep cycles, which can occur if different processes are sleeping on the same address accidentally. If you set the PCATCH flag in the pri argument, the sleep routine puts signals on the queue and does not wake up the sleeping process. The sleep and wakeup routines block and then wake up a process. Generally, device drivers call these routines to wait for the transfer to complete an interrupt from the device. That is, the write routine of the device driver sleeps on the address of a known location, and the device's Interrupt Service Interface (ISI) wakes the process when the device interrupts. It is the responsibility of the wakened process to check if the condition for which it was sleeping has been removed. NOTES
The operating system provides two ways to put a process to sleep: interruptible and uninterruptible. The sleep routine performs an uninter- ruptible sleep operation if you do not set the PCATCH flag and an interruptible sleep operation if you set the PCATCH flag. This means that device drivers cannot call sleep at interrupt context because at interrupt context there is no calling process to be put to sleep. Thus, a device driver's Interrupt Service Interface (ISI) and those routines called from within the ISI must not call the sleep routine. On this operating system, you cannot use pri to set the scheduling priority of the calling process. RETURN VALUES
None FILES
SEE ALSO
Routines: wakeup(9r) sleep(9r)