On Fri, May 09, 2014 at 03:55:14PM -0700, Paul E. McKenney wrote: > On Fri, May 09, 2014 at 03:40:52PM -0700, Josh Triplett wrote: > > On Fri, May 09, 2014 at 03:30:04PM -0700, Paul E. McKenney wrote: > > > On Fri, May 09, 2014 at 12:32:46PM -0700, Josh Triplett wrote: > > > > 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.) > > > > > > But that would require me to provide these same exports from TINY_RCU, > > > which does not need them. > > > > > > How about exporting integers identifying the flavors of RCU to rcutorture, > > > which rcutorture can then pass to rcutorture_get_gp_data()? This allows > > > TINY_RCU to provide a trivial static inline function. TREE_RCU and > > > TREE_PREEMPT_RCU can keep an array of pointers to the corresponding > > > rcu_state structure, with NULL pointers for flavors of RCU that don't > > > have any data to provide. > > > > > > Would that help? > > > > Either way seems fine: a single function with an extra parameter or a > > unique function per flavor. But if you're going to provide the > > RCU-flavor integers, they should be in RCU itself and refer to RCU > > flavors, rather than being in rcutorture and refering to test types. > > Fair enough, will take that approach! > > I am thinking in terms of something like the following: > > RCU_FLAVOR > RCU_BH_FLAVOR > RCU_SCHED_FLAVOR > SRCU_FLAVOR > OTHER_FLAVOR > > The "OTHER_FLAVOR" would be what rcutorture uses for the "busted" > incorrect-on-purpose flavor of RCU, which is local to rcutorture. > > Seem reasonable, or would some other naming scheme be better?
Seems reasonable to me. I'd call the last one "INVALID_RCU_FLAVOR" or similar. - 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/
