[lkml]   [2008]   [Nov]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 3/3] tracing/function-return-tracer: add the overrun field
2008/11/21 Ingo Molnar <>:
> * Frédéric Weisbecker <> wrote:
>> When the tracer will be launched, I will hold the tasklist_lock to
>> allocate/insert the dynamic arrays. So in this atomic context, I
>> will not be able to call kmalloc with GFP_KERNEL. And I fear that
>> using GFP_ATOMIC for possible hundreds of tasks would be clearly
>> unacceptable.
>> What do you think of this way:
>> _tracer activates
>> _a function enters the tracer entry-hooker. If the array is allocated
>> for the current task, that's well. If not I launch a kernel thread
>> that will later allocate an array for the current task (I will pass
>> the pid as a parameter). So the current task will be soon be traced.
>> _ when a process forks, I can allocate a dynamic array for the new
>> task without problem (I hope).
>> So some tasks will not be traced at the early beggining of tracing
>> but they will soon all be traced.... There is perhaps a problem with
>> tasks that are sleeping for long times... There will be some losses
>> once they will be awaken...
> i'd suggest a different approach that is simpler:
> - step0: set flag that "all newly created tasks need the array
> allocated from now on".
> - step1: allocate N arrays outside tasklist_lock
> - step2: take tasklist_lock, loop over all tasks that exist and pass
> in the N arrays to all tasks that still need it.
> If tasks were 'refilled', drop tasklist_lock and go back to step 1.
> - step3: free N (superfluously allocated) arrays
> Make N something like 32 to not get into a bad quadratic nr_tasks
> double loop in practice. (Possibly allocate arrays[32] dynamically as
> well at step0 and not have it on the kernel stack - so 32 can be
> changed to 128 or so.)
> Ingo

Ok. I thought about this method but wondered about the fact that
kmalloc can schedule and then I could run in an infinite loop (or a
too long one).
I will try this. Thanks.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2008-11-21 21:09    [W:0.070 / U:1.680 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site