On Fri, May 09, 2014 at 10:36:58AM -0700, Paul E. McKenney wrote: > On Fri, May 09, 2014 at 08:52:31AM -0700, Josh Triplett wrote: > > On Wed, May 07, 2014 at 04:43:13PM -0700, Paul E. McKenney wrote: > > > On Wed, May 07, 2014 at 02:16:49PM -0700, j...@joshtriplett.org wrote: > > > > On Mon, Apr 28, 2014 at 05:24:49PM -0700, Paul E. McKenney wrote: > > > > > From: "Paul E. McKenney" <paul...@linux.vnet.ibm.com> > > > > > > > > > > The rcutorture output currently does not distinguish between stalls in > > > > > the RCU implementation and stalls in the rcu_torture_writer() > > > > > kthreads. > > > > > This commit therefore adds some diagnostics to help distinguish > > > > > between > > > > > these two conditions, at least for the non-SRCU implementations. > > > > > (SRCU > > > > > does not provide evidence of update-side forward progress by design.) > > > > > > > > > > Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com> > > > > > > > > The concept makes sense, and the writer state annotations seem like a > > > > useful debugging mechanism, but having RCU know about RCU torture types > > > > seems fundamentally wrong. This mechanism accesses rcu_state, which is > > > > already implementation-specific, so why not just only define the > > > > function for the RCU implementations that support it, and then have a > > > > function pointer in the torture-test structure to report a stall? > > > > > > Ouch. It is worse than that! When running RCU-bh or RCU-sched, > > > the current code incorrectly returns the statistics for RCU. > > > So I do need some way for rcutorture to tell RCU which flavor > > > it is testing. > > > > > > One thing I could do would be to pass in a pointer to the call_rcu() > > > function (cur_ops->call from rcutorture's viewpoint), then scan the > > > rcu_state structures looking for the selected flavor (rsp->call from > > > tree.c's viewpoint). In the SRCU and RCU-busted cases, the flavor would > > > not be found, and I could then just set everything to zero. > > > > > > Does that seem reasonable, or is there a better way to do this? > > > > That search seems rather too hackish; why not just declare one > > stats-returning function per RCU flavor, and put the pointer to the > > corresponding function in the structure for each test type? > > The problem is that rcutorture doesn't know anything about the structures, > as those are internal to the implementation. All it knows is which > functions it is using. I -could- EXPORT_SYMBOL_GPL() the rcu_state > structures to modules (they are already non-static), then rename > TINY_RCU's rcu_ctrlblk to rcu_state to allow the needed type punning, > then do some special-case thing for SRCU, and put a pointer to whatever > in rcu_torture_ops, but that was feeling a bit hackish as well. > > So what did you have in mind to allow rcutorture to communicate the > rcuflavor to the underlying RCU implementation?
Rather than EXPORT_SYMBOL_GPLing the rcu_state structures, just EXPORT_SYMBOL_GPL one version of rcutorture_get_gp_data per RCU flavor. (And hide them all behind #ifdef CONFIG_RCU_TORTURE_TEST.) Then add a get_gp_data field to rcu_torture_ops; if NULL, skip the stats. (Or put a no-op version in rcutorture.) - Josh Triplett -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
