On Fri, Aug 2, 2024 at 3:02 AM Yunsheng Lin <linyunsheng@xxxxxxxxxx> wrote: > > 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. Right. That is more or less what I was thinking. > > > >> > >>> > >>> 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. Right now you can't compile it as built-in anyway and you were returning EAGAIN. If you are going that route then it makes more sense to compile it outside of the mm tree since it isn't a valid module in the first place. > > > >>> 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. That is why I am suggesting either fix the module so that it can be compiled in, or move it to selftest. The current module is not a valid one and doesn't belong here in its current form. > > > >>> 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 That is fine. If that is the case then it should be in the selftest folder. > > 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? Yes, I would be fine with it in that case.
