On 2024/8/1 22:50, Alexander Duyck wrote: >> >> The above was my initial thinking too, I went to the ptrpool thing using >> at least two CPUs as the below reason: >> 1. Test the concurrent calling between allocing and freeing more throughly, >> for example, page->_refcount concurrent handling, cache draining and >> cache reusing code path will be tested more throughly. >> 2. Test the performance impact of cache bouncing between different CPUs. >> >> I am not sure if there is a more lightweight implementation than ptrpool >> to do the above testing more throughly. > > You can still do that with a single producer single consumer ring > buffer/array and not have to introduce a ton of extra overhead for > some push/pop approach. There are a number of different > implementations for such things throughout the kernel. if we limit that to single producer single consumer, it seems we can use ptr_ring to replace ptrpool. > >> >>> >>> Lastly something that is a module only tester that always fails to >>> probe doesn't sound like it really makes sense as a standard kernel >> >> I had the same feeling as you, but when doing testing, it seems >> convenient enough to do a 'insmod xxx.ko' for testing without a >> 'rmmod xxx.ko' > > It means this isn't a viable module though. If it supports insmod to > trigger your tests you should let it succeed, and then do a rmmod to > remove it afterwards. Otherwise it is a test module and belongs in the > selftest block. > >>> module. I still think it would make more sense to move it to the >>> selftests tree and just have it build there as a module instead of >> >> I failed to find one example of test kernel module that is in the >> selftests tree yet. If it does make sense, please provide an example >> here, and I am willing to follow the pattern if there is one. > > You must not have been looking very hard. A quick grep for > "module_init" in the selftest folder comes up with > "tools/testing/selftests/bpf/bpf_testmod/" containing an example of a > module built in the selftests folder. After close look, it seems it will be treated as third party module when adding a kernel module in tools/testing/selftests as there seems to be no config for it in Kconfig file and can only be compiled as a module not as built-in. > >>> trying to force it into the mm tree. The example of dmapool_test makes >>> sense as it could be run at early boot to run the test and then it >> >> I suppose you meant dmapool is built-in to the kernel and run at early >> boot? I am not sure what is the point of built-in for dmapool, as it >> only do one-time testing, and built-in for dmapool only waste some >> memory when testing is done. > > There are cases where one might want to test on a system w/o console > access such as an embedded system, or in the case of an environment > where people run without an initrd at all. I think moving it to tools/testing/selftests may defeat the above purpose. > >>> just goes quiet. This module won't load and will always just return >>> -EAGAIN which doesn't sound like a valid kernel module to me. >> >> As above, it seems convenient enough to do a 'insmod xxx.ko' for testing >> without a 'rmmod xxx.ko'. > > It is, but it isn't. The problem is it creates a bunch of ugliness in Yes, it seems a bit ugly, but it supports the below perf cmd, I really would like to support the below case as it is very convenient. perf stat -r 200 -- insmod ./page_frag_test.ko test_push_cpu=16 test_pop_cpu=17 > the build as you are a tristate that isn't a tristate as you are only > building it if it is set to "m". There isn't anything like that > currently in the mm tree. After moving page_frag_test to selftest, it is only bulit as module, I guess it is ok to return -EAGAIN?
