Messages in this thread | | | Date | Sun, 23 Nov 2008 14:18:50 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 3/3] tracing/function-return-tracer: add the overrun field |
| |
* Frédéric Weisbecker <fweisbec@gmail.com> wrote:
> 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).
the retry loop should solve that aspect - and the chunking solves the "dont run too long with a lock held" problem.
> I will try this. Thanks.
looks good, applied :)
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/
| |