Messages in this thread | | | Date | Thu, 21 Aug 2008 14:26:04 -0400 (EDT) | From | Steven Rostedt <> | Subject | Re: ftraced and suspend to ram |
| |
On Thu, 21 Aug 2008, Rafael J. Wysocki wrote:
> On Thursday, 21 of August 2008, Steven Rostedt wrote: > > > > In latest 2.6.27(git) enabling dynamic ftrace makes resume from a suspend > > to ram reboot instead of resuming. Queued for 2.6.28 is a new method of > > recording mcount callers at compile time that does not have this issue. > > > > But the new method is still too "green" to be pulled into 27, so the old > > ftraced (daemon method) needs to be fixed for 27. > > > > The way dynamic ftrace works with the daemon method is this. On boot up > > the mcount function simply returns. When ftrace is initialized, it calls > > kstop_machine to modify the mcount function to call another function > > called "ftrace_record_ip". This new function will record in a preallocated > > hash (allocated by the ftrace initializer) all the callers of mcount. A > > check is made to see if the caller has already been put into the hash, and > > if so, it is not recorded again. > > > > Later on a kernel thread ftraced is created. This kernel thread wakes up > > once a second and checks to see if any new functions were added to the > > hash. If so, it then calls kstop_machine and modifies those callers to > > mcount into nops. > > > > Again, this daemon method makes resume from suspend to ram reboot instead > > of resuming. Now, I'm asking the s2r gurus, what did I miss? Do I need to > > add a "NO_FREEZE" flag or something to the "ftraced" kernel thread? > > > > Just asking for some advice. > > If I'm not mistaken, it'll probably suffice to make it freezable, so that it > doesn't run while the system is suspending and resuming. Would that be > acceptable?
Does it not freeze by default.
> > Please tell me where exactly the ftraced source code is located.
It's in Linus's latest git tree.
The code in question is the ftraced() function in kernel/trace/ftrace.c
Thanks,
-- Steve
| |