On Fri, Aug 2, 2024 at 3:02 AM Yunsheng Lin [off-list ref] wrote:
On 2024/8/1 22:50, Alexander Duyck wrote:
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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.
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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.
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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.
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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.
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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.
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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.