On Fri, 4 Apr 2008, Nikhil Talpallikar wrote:
> On Fri, Apr 4, 2008 at 10:23 PM, Robert P. J. Day <[EMAIL PROTECTED]>
> wrote:
>
> >
> > i'm still a bit unclear on the linked list traversal of kernel
> > "tasks", given what i'm reading in some documentation someone sent me,
> > and i'm thinking that this doc isn't quite correct.
> >
> > the bullet points in this doc (whose identity shall remain
> > concealed, to protect the innocent :-):
> >
> > * Only default threads linked by tasks list_head
> > * Other threads not seen by for_each_process() macro
> > * Visible to do_each_thread() macro
> >
> > now, if by "default thread" the author means the thread group
> > leader, this doesn't seem right, does it? that clearly suggests that
> > only each thread group leader is on the system-wide task list. i
> > thought someone on this (mailing) list had already taken the position
> > that, no, *all* threads need to be on the system-wide task list for
> > proper scheduling.
> >
> > and it gets more confusing if you examine the definition of those
> > macros in sched.h:
> >
> > ====================
> > #define next_task(p) \
> > list_entry(rcu_dereference((p)->tasks.next), struct task_struct,
> > tasks)
> >
> > #define for_each_process(p) \
> > for (p = &init_task ; (p = next_task(p)) != &init_task ; )
> >
> > /*
> > * Careful: do_each_thread/while_each_thread is a double loop so
> > * 'break' will not work as expected - use goto instead.
> > */
> > #define do_each_thread(g, t) \
> > for (g = t = &init_task ; (g = t = next_task(g)) != &init_task ; )
> > do
>
>
> this is a double loop
>
> #define while_each_thread(g,t) \
> while ((t = next_thread(t) != g)
>
> this leads to the conclusion.....the document ur reading document is
> correct.
ah, i get it -- i didn't look closely enough at the actual
*invocation* of those macros -- you're supposed to use
do_each_thread() and while_each_thread() in pairs on a single loop, as
in:
do_each_thread(g, p) {
/*
* reset the NMI-timeout, listing all files on a slow
* console might take alot of time:
*/
touch_nmi_watchdog();
if (!state_filter || (p->state & state_filter))
sched_show_task(p);
} while_each_thread(g, p);
my fault, sorry for the noise. must read more carefully next time.
rday
--
========================================================================
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry:
Have classroom, will lecture.
http://crashcourse.ca Waterloo, Ontario, CANADA
========================================================================
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