From: Mina Almasry <almasrymina@google.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: "David Wei" <dw@davidwei.uk>,
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Subject: Re: [RFC PATCH net-next v8 07/14] page_pool: devmem support
Date: Tue, 30 Apr 2024 12:19:17 -0700 [thread overview]
Message-ID: <CAHS8izP3KtH_CHyQKE+=vrY-yREq5Bb_Kd+KLyJ4j-_AdjNk-Q@mail.gmail.com> (raw)
In-Reply-To: <11f52113-7b67-4b45-ba1d-29b070050cec@kernel.dk>
On Tue, Apr 30, 2024 at 11:55 AM Jens Axboe <axboe@kernel.dk> wrote:
>
> On 4/30/24 12:29 PM, Mina Almasry wrote:
> > On Tue, Apr 30, 2024 at 6:46?AM Jens Axboe <axboe@kernel.dk> wrote:
> >>
> >> On 4/26/24 8:11 PM, Mina Almasry wrote:
> >>> On Fri, Apr 26, 2024 at 5:18?PM David Wei <dw@davidwei.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.
> >>
> >> In general, attempting to hide overhead behind config options is always
> >> a losing proposition. It merely serves to say "look, if these things
> >> aren't enabled, the overhead isn't there", while distros blindly enable
> >> pretty much everything and then you're back where you started.
> >>
> >
> > The history there is that this check adds 1 cycle regression to the
> > page_pool fast path benchmark. The regression last I measured is 8->9
> > cycles, so in % wise it's a quite significant 12.5% (more details in
> > the cover letter[1]). I doubt I can do much better than that to be
> > honest.
>
> I'm all for cycle counting, and do it myself too, but is that even
> measurable in anything that isn't a super targeted microbenchmark? Or
> even in that?
>
Not as far as I can tell, no. This was purely to improve the page_pool
benchmark.
> > There was a desire not to pay this overhead in setups that will likely
> > not care about devmem, like embedded devices maybe, or setups without
> > GPUs. Adding a CONFIG check here seemed like very low hanging fruit,
> > but yes it just hides the overhead in some configs, not really removes
> > it.
> >
> > There was a discussion about adding this entire netmem/devmem work
> > under a new CONFIG. There was pushback particularly from Willem that
> > at the end of the day what is enabled on most distros is what matters
> > and we added code churn and CONFIG churn for little value.
> >
> > If there is significant pushback to the CONFIG check I can remove it.
> > I don't feel like it's critical, it just mirco-optimizes some setups
> > that doesn't really care about this work area.
>
> That is true, but in practice it'll be enabled anyway. Seems like it's
> not really worth it in this scenario.
>
OK, no pushback from me. I'll remove the CONFIG check in the next iteration.
--
Thanks,
Mina
next prev parent reply other threads:[~2024-04-30 19:19 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-03 0:20 [RFC PATCH net-next v8 00/14] Device Memory TCP Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 01/14] queue_api: define queue api Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 02/14] net: page_pool: create hooks for custom page providers Mina Almasry
[not found] ` <ZjH1QaSSQ98mw158@infradead.org>
2024-05-03 20:10 ` Mina Almasry
[not found] ` <ZjjHUh1eINPg1wkn@infradead.org>
2024-05-07 16:05 ` Pavel Begunkov
2024-05-07 16:18 ` Jason Gunthorpe
[not found] ` <ZjpVfPqGNfE5N4bl@infradead.org>
2024-05-07 16:42 ` Mina Almasry
2024-05-07 16:48 ` Jason Gunthorpe
2024-05-07 17:19 ` Daniel Vetter
2024-05-07 17:25 ` Pavel Begunkov
2024-05-07 17:56 ` Jason Gunthorpe
2024-05-07 19:35 ` Pavel Begunkov
2024-05-07 23:32 ` Jason Gunthorpe
2024-05-08 7:16 ` Daniel Vetter
2024-05-08 11:35 ` Pavel Begunkov
2024-05-08 15:34 ` Daniel Vetter
[not found] ` <ZjufddNVJs5Csaix@infradead.org>
2024-05-08 17:02 ` Pavel Begunkov
2024-05-08 11:30 ` Pavel Begunkov
2024-05-08 14:25 ` Jason Gunthorpe
2024-05-08 15:44 ` Pavel Begunkov
2024-05-08 15:58 ` Jason Gunthorpe
2024-05-08 16:13 ` Pavel Begunkov
2024-05-07 17:17 ` Pavel Begunkov
2024-05-07 16:55 ` Pavel Begunkov
2024-05-07 17:15 ` Mina Almasry
2024-05-07 17:34 ` Pavel Begunkov
2024-04-03 0:20 ` [RFC PATCH net-next v8 03/14] net: netdev netlink api to bind dma-buf to a net device Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 04/14] netdev: support binding dma-buf to netdevice Mina Almasry
2024-04-24 17:35 ` David Wei
2024-04-24 22:11 ` Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 05/14] netdev: netdevice devmem allocator Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 06/14] page_pool: convert to use netmem Mina Almasry
2024-04-03 17:27 ` Simon Horman
2024-04-03 0:20 ` [RFC PATCH net-next v8 07/14] page_pool: devmem support Mina Almasry
2024-04-27 0:17 ` David Wei
2024-04-27 2:11 ` Mina Almasry
2024-04-30 13:31 ` Pavel Begunkov
2024-04-30 13:45 ` Jens Axboe
2024-04-30 18:29 ` Mina Almasry
2024-04-30 18:55 ` Jens Axboe
2024-04-30 19:19 ` Mina Almasry [this message]
2024-05-01 13:58 ` Jesper Dangaard Brouer
[not found] ` <ZjH1hO8qJgOqNKub@infradead.org>
2024-05-06 0:29 ` David Wei
2024-04-03 0:20 ` [RFC PATCH net-next v8 08/14] memory-provider: dmabuf devmem memory provider Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 09/14] net: support non paged skb frags Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 10/14] net: add support for skbs with unreadable frags Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 11/14] tcp: RX path for devmem TCP Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 12/14] net: add SO_DEVMEM_DONTNEED setsockopt to release RX frags Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 13/14] net: add devmem TCP documentation Mina Almasry
2024-05-03 13:14 ` Bagas Sanjaya
2024-04-03 0:20 ` [RFC PATCH net-next v8 14/14] selftests: add ncdevmem, netcat for devmem TCP Mina Almasry
2024-04-08 15:57 ` Cong Wang
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