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McKenney writes: > On Thu, Feb 15, 2024 at 01:24:59PM -0800, Ankur Arora wrote: >> >> Paul E. McKenney writes: >> >> > On Wed, Feb 14, 2024 at 07:45:18PM -0800, Paul E. McKenney wrote: >> >> On Wed, Feb 14, 2024 at 06:03:28PM -0800, Ankur Arora wrote: >> >> > >> >> > Paul E. McKenney writes: >> >> > >> >> > > On Mon, Feb 12, 2024 at 09:55:24PM -0800, Ankur Arora wrote: >> >> > >> Hi, >> >> > >> >> >> > >> This series adds a new scheduling model PREEMPT_AUTO, which like >> >> > >> PREEMPT_DYNAMIC allows dynamic switching between a none/voluntary/full >> >> > >> preemption model. However, unlike PREEMPT_DYNAMIC, it doesn't depend >> >> > >> on explicit preemption points for the voluntary models. >> >> > >> >> >> > >> The series is based on Thomas' original proposal which he outlined >> >> > >> in [1], [2] and in his PoC [3]. >> >> > >> >> >> > >> An earlier RFC version is at [4]. >> >> > > >> >> > > This uncovered a couple of latent bugs in RCU due to its having been >> >> > > a good long time since anyone built a !SMP preemptible kernel with >> >> > > non-preemptible RCU. I have a couple of fixes queued on -rcu [1], most >> >> > > likely for the merge window after next, but let me know if you need >> >> > > them sooner. >> >> > >> >> > Thanks. As you can probably tell, I skipped out on !SMP in my testing. >> >> > But, the attached diff should tide me over until the fixes are in. >> >> >> >> That was indeed my guess. ;-) >> >> >> >> > > I am also seeing OOM conditions during rcutorture testing of callback >> >> > > flooding, but I am still looking into this. >> >> > >> >> > That's on the PREEMPT_AUTO && PREEMPT_VOLUNTARY configuration? >> >> >> >> On two of the PREEMPT_AUTO && PREEMPT_NONE configurations, but only on >> >> two of them thus far. I am running a longer test to see if this might >> >> be just luck. If not, I look to see what rcutorture scenarios TREE10 >> >> and TRACE01 have in common. >> > >> > And still TRACE01 and TREE10 are hitting OOMs, still not seeing what >> > sets them apart. I also hit a grace-period hang in TREE04, which does >> > CONFIG_PREEMPT_VOLUNTARY=y along with CONFIG_PREEMPT_AUTO=y. Something >> > to dig into more. >> >> So, the only PREEMPT_VOLUNTARY=y configuration is TREE04. I wonder >> if you would continue to hit the TREE04 hang with CONFIG_PREEMTP_NONE=y >> as well? >> (Just in the interest of minimizing configurations.) > > I would be happy to, but in the spirit of full disclosure... > > First, I have seen that failure only once, which is not enough to > conclude that it has much to do with TREE04. It might simply be low > probability, so that TREE04 simply was unlucky enough to hit it first. > In contrast, I have sufficient data to be reasonably confident that the > callback-flooding OOMs really do have something to do with the TRACE01 and > TREE10 scenarios, even though I am not yet seeing what these two scenarios > have in common that they don't also have in common with other scenarios. > But what is life without a bit of mystery? ;-) :). > Second, please see the attached tarball, which contains .csv files showing > Kconfig options and kernel boot parameters for the various torture tests. > The portions of the filenames preceding the "config.csv" correspond to > the directories in tools/testing/selftests/rcutorture/configs. So, at least some of the HZ_FULL=y tests don't run into problems. > Third, there are additional scenarios hand-crafted by the script at > tools/testing/selftests/rcutorture/bin/torture.sh. Thus far, none of > them have triggered, other than via the newly increased difficulty > of configurating a tracing-free kernel with which to test, but they > can still be useful in ruling out particular Kconfig options or kernel > boot parameters being related to a given issue. > > But please do take a look at the .csv files and let me know what > adjustments would be appropriate given the failure information. Nothing stands out just yet. Let me start a run here and see if that gives me some ideas. I'm guessing the splats don't give any useful information or you would have attached them ;). Thanks for testing, btw. -- ankur