netdev - Re: [PATCH net-next v2 1/2] selftests/ptr_ring: add benchmark application for ptr

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Date:   Mon, 28 Jun 2021 09:42:06 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     Jason Wang <jasowang@...hat.com>, <davem@...emloft.net>,
        <kuba@...nel.org>, <brouer@...hat.com>, <paulmck@...nel.org>,
        <peterz@...radead.org>, <will@...nel.org>, <shuah@...nel.org>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>, <linuxarm@...neuler.org>
Subject: Re: [PATCH net-next v2 1/2] selftests/ptr_ring: add benchmark
 application for ptr_ring

On 2021/6/27 14:09, Michael S. Tsirkin wrote:
> On Fri, Jun 25, 2021 at 11:52:16AM +0800, Yunsheng Lin wrote:
>> On 2021/6/25 11:36, Jason Wang wrote:
>>>
>>> 在 2021/6/25 上午11:18, Yunsheng Lin 写道:
>>>> Currently ptr_ring selftest is embedded within the virtio
>>>> selftest, which involves some specific virtio operation,
>>>> such as notifying and kicking.
>>>>
>>>> As ptr_ring has been used by various subsystems, it deserves
>>>> it's owner's selftest in order to benchmark different usecase
>>>> of ptr_ring, such as page pool and pfifo_fast qdisc.
>>>>
>>>> So add a simple application to benchmark ptr_ring performance.
>>>> Currently two test mode is supported:
>>>> Mode 0: Both enqueuing and dequeuing is done in a single thread,
>>>>          it is called simple test mode in the test app.
>>>> Mode 1: Enqueuing and dequeuing is done in different thread
>>>>          concurrently, also known as SPSC(single-producer/
>>>>          single-consumer) test.
>>>>
>>>> The multi-producer/single-consumer test for pfifo_fast case is
>>>> not added yet, which can be added if using CAS atomic operation
>>>> to enable lockless multi-producer is proved to be better than
>>>> using r->producer_lock.
>>>>
>>>> Only supported on x86 and arm64 for now.
>>>>
>>>> Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com>
>>>> ---
>>>>   MAINTAINERS                                      |   5 +
>>>>   tools/testing/selftests/ptr_ring/Makefile        |   6 +
>>>>   tools/testing/selftests/ptr_ring/ptr_ring_test.c | 249 +++++++++++++++++++++++
>>>>   tools/testing/selftests/ptr_ring/ptr_ring_test.h | 150 ++++++++++++++
>>>>   4 files changed, 410 insertions(+)
>>>
>>>
>>> Why can't you simply reuse tools/virtio/ringtest?
>>
>> The main reason is stated in the commit log:
>> "Currently ptr_ring selftest is embedded within the virtio
>> selftest, which involves some specific virtio operation,
>> such as notifying and kicking.
>>
>> As ptr_ring has been used by various subsystems, it deserves
>> it's owner's selftest in order to benchmark different usecase
>> of ptr_ring, such as page pool and pfifo_fast qdisc."
>>
>> More specificly in tools/virtio/ringtest/main.c and
>> tools/virtio/ringtest/ptr_ring.c, there are a lot of operation
>> related to virtio usecase, such as start_guest(), start_host(),
>> poll_used(), notify() or kick() ....., so it makes more sense
>> to add a generic selftest for ptr ring as it is not only used
>> by virtio now.
> 
> 
> Okay that answers why you didn't just run main.c
> but why not add a new test under tools/virtio/ringtest/
> reusing the rest of infrastructure that you currently copied?

Actually, my first attempt was to reuse the infrastructure in
tools/virtio/ or tools/virtio/ringtest/, and neither of them
was able to be compiled in the latest kernel.

And then I read through the code to try fixing the compile error,
I found that the testcase under tools/virtio/ is coupled deeply
to virtio as explained above, which was difficult to read for
someone who is not fimiliar with virtio.

So I searched for how testing is supposed to be added in the kernel,
it seems it is more common to add the testing in tools/testing or
tools/testing/selftest, and ptr ring is not only used by virtio now,
so it seems more appropriate to add a sperate testing for virtio by
instinct.

Most of tools/virtio/ is to do testing related to virtio testing, IMHO,
most of them are better to be in tools/testing/selftest. Even if most of
virtio testing is moved to tools/testing/selftest, I think it makes more
sense to decouple the virtio testing to ptr_ring testing too if we can
find some mechanism to share the abstract infrastructure in ptr_ring_test.h
for both virtio and ptr_ring testing.


> 
>>
>>>
>>> Thanks
>>>
>>>
>>> .
>>>
> 
> 
> .
>