Messages in this thread | | | Date | Fri, 21 Nov 2008 20:48:19 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 3/3] tracing/function-return-tracer: add the overrun field |
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* Frédéric Weisbecker <fweisbec@gmail.com> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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