Messages in this thread | | | Date | Thu, 21 Aug 2008 11:49:45 -0400 (EDT) | From | Steven Rostedt <> | Subject | ftraced and suspend to ram |
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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.
Thanks,
-- Steve
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