Messages in this thread | | | Date | Fri, 21 Nov 2008 21:07:33 +0100 | From | "Frédéric Weisbecker" <> | Subject | Re: [PATCH 3/3] tracing/function-return-tracer: add the overrun field |
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2008/11/21 Ingo Molnar <mingo@elte.hu>: > > * 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 >
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 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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