linux-kernel - Re: [RFC PATCH net-next v8 07/14] page

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Message-ID: <CAHS8izPeYryoLdCAQdGQU-wn7YVdtuofVKNvRFjFjhqTDsT7zA@mail.gmail.com>
Date: Fri, 26 Apr 2024 19:11:07 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: David Wei <dw@...idwei.uk>
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Subject: Re: [RFC PATCH net-next v8 07/14] page_pool: devmem support

On Fri, Apr 26, 2024 at 5:18 PM David Wei <dw@...idwei.uk> wrote:
>
> On 2024-04-02 5:20 pm, Mina Almasry wrote:
> > @@ -69,20 +106,26 @@ net_iov_binding(const struct net_iov *niov)
> >   */
> >  typedef unsigned long __bitwise netmem_ref;
> >
> > +static inline bool netmem_is_net_iov(const netmem_ref netmem)
> > +{
> > +#if defined(CONFIG_PAGE_POOL) && defined(CONFIG_DMA_SHARED_BUFFER)
>
> I am guessing you added this to try and speed up the fast path? It's
> overly restrictive for us since we do not need dmabuf necessarily. I
> spent a bit too much time wondering why things aren't working only to
> find this :(

My apologies, I'll try to put the changelog somewhere prominent, or
notify you when I do something that I think breaks you.

Yes, this is a by-product of a discussion with regards to the
page_pool benchmark regressions due to adding devmem. There is some
background on why this was added and the impact on the
bench_page_pool_simple tests in the cover letter.

For you, I imagine you want to change this to something like:

#if defined(CONFIG_PAGE_POOL)
#if defined(CONFIG_DMA_SHARED_BUFFER) || defined(CONFIG_IOURING)

or something like that, right? Not sure if this is something I should
do here or if something more appropriate to be in the patches you
apply on top.

I additionally think you may also need to run the
page_pool_benchmark_simple tests like I do in the cover letter to see
if you're affecting those.

--
Thanks,
Mina