On 11/19/2018 10:17 AM, Qian Cai wrote: > On Mon, 2018-11-19 at 09:51 -0500, Waiman Long wrote: >> On 11/19/2018 08:27 AM, Qian Cai wrote: >>> On 11/19/18 at 3:09 AM, Thomas Gleixner wrote: >>> >>>> Qian, >>>> >>>> On Sun, 18 Nov 2018, Qian Cai wrote: >>>>>> On Nov 18, 2018, at 1:21 PM, Thomas Gleixner <t...@linutronix.de> >>>>>> wrote: >>>>>> On Sun, 18 Nov 2018, Qian Cai wrote: >>>>>>> As the results, systems have 60+ CPUs with both timer and workqueue >>>>>>> objects enabled could trigger "ODEBUG: Out of memory. ODEBUG >>>>>>> disabled". >>>>>>> >>>>>>> Hence, add a new Kconfig option so users could adjust >>>>>>> ODEBUG_POOL_SIZE >>>>>>> accordingly if either timer or workqueue objects are selected. >>>>>> why do we need a config option, when the required number can be >>>>>> deduced >>>>>> already from the active CONFIG_DEBUG_OBJECTS_* and NR_CPUS? >>>>>> >>>>> It because I am worry about the coupling between the implementation >>>>> details of >>>>> timers and workqueue objects, and the computation in the code you >>>>> mentioned >>>>> here. For example, people could change workqueue.c to have different >>>>> number >>>>> of worekqueues initialized during the early boot in the future which is >>>>> going to >>>>> affect the required pool size, and I am not sure if people are going to >>>>> adjust the >>>>> code in debugobjects.c here as well when they made changes like that. >>>>> >>>>> Also, the computation could become so complex depends on lots of config >>>>> options like perf, hrtimer, and combinations that I have not tested so >>>>> far which is >>>>> difficult to exhausted all the possibilities. >>>>> >>>>> Hence, I feel like the Kconfig option is more flexible and less error- >>>>> prone. >>>> Quite the contrary. Config options are a pain and truly error-prone if you >>>> want to compile general purpose kernels as distributions do. >>>> >>> Ah, I never thought distributions people would >>> enable those debugging options. >> Distros like RHEL usually ship two kernels - one for production and one >> for debug. The debug kernel does have debugobjects enabled. >> > Right, I can remember that now . However, if I understand correctly, since the > early static pool size needs to be determined during the compilation time, it > depends on the No. CPUs are from the machines that built the distro kernels. > Then, when users use those distro kernels, they are not going to have correct > the pool size according to the No. CPUs on their test machines.
I see your point. Perhaps you can make ODEBUG_POOL_SIZE scales with CONFIG_NR_CPUS like #define ODEBUG_POOL_SIZE (1024 + CONFIG_NR_CPUS * 2) CONFIG_NR_CPUS is usually set to a lot higher than the actual number of CPUs in a typical system. So you don't want to set the multiplier too high. Cheers, Longman
