From: John Fastabend <john.fastabend@gmail.com>
To: "Alexander Lobakin" <aleksander.lobakin@intel.com>,
"Toke Høiland-Jørgensen" <toke@redhat.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <martin.lau@linux.dev>,
Eduard Zingerman <eddyz87@gmail.com>,
Song Liu <song@kernel.org>,
Yonghong Song <yonghong.song@linux.dev>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@google.com>,
Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Jesper Dangaard Brouer <hawk@kernel.org>,
Eric Dumazet <edumazet@google.com>,
Paolo Abeni <pabeni@redhat.com>,
bpf@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [PATCH net-next v2 2/4] bpf: test_run: Use system page pool for XDP live frame mode
Date: Wed, 03 Apr 2024 13:39:35 -0700 [thread overview]
Message-ID: <660dbe87d8797_1cf6b2083c@john.notmuch> (raw)
In-Reply-To: <2746b1d9-2e1f-4e66-89ed-19949a189a92@intel.com>
Alexander Lobakin wrote:
> From: Toke Høiland-Jørgensen <toke@redhat.com>
> Date: Tue, 20 Feb 2024 22:03:39 +0100
>
> > The BPF_TEST_RUN code in XDP live frame mode creates a new page pool
> > each time it is called and uses that to allocate the frames used for the
> > XDP run. This works well if the syscall is used with a high repetitions
> > number, as it allows for efficient page recycling. However, if used with
> > a small number of repetitions, the overhead of creating and tearing down
> > the page pool is significant, and can even lead to system stalls if the
> > syscall is called in a tight loop.
> >
> > Now that we have a persistent system page pool instance, it becomes
> > pretty straight forward to change the test_run code to use it. The only
> > wrinkle is that we can no longer rely on a custom page init callback
> > from page_pool itself; instead, we change the test_run code to write a
> > random cookie value to the beginning of the page as an indicator that
> > the page has been initialised and can be re-used without copying the
> > initial data again.
> >
> > The cookie is a random 128-bit value, which means the probability that
> > we will get accidental collisions (which would lead to recycling the
> > wrong page values and reading garbage) is on the order of 2^-128. This
> > is in the "won't happen before the heat death of the universe" range, so
> > this marking is safe for the intended usage.
> >
> > Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
> > Tested-by: Alexander Lobakin <aleksander.lobakin@intel.com>
> > Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
>
> Hey,
>
> What's the status of this series, now that the window is open?
>
> Thanks,
> Olek
Hi Toke,
I read the thread from top to bottom so seems someone else notices the
2^128 is unique numbers not the collision probability. Anywaays I'm still
a bit confused, whats the use case here? Maybe I need to understand
what this XDP live frame mode is better?
Could another solution be to avoid calling BPF_TEST_RUN multiple times
in a row? Or perhaps have a BPF_SETUP_RUN that does the config and lets
BPF_TEST_RUN skip the page allocation? Another idea just have the first
run of BPF_TEST_RUN init a page pool and not destroy it.
Thanks,
John
next prev parent reply other threads:[~2024-04-03 20:39 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-20 21:03 [PATCH net-next v2 0/4] Change BPF_TEST_RUN use the system page pool for live XDP frames Toke Høiland-Jørgensen
2024-02-20 21:03 ` [PATCH net-next v2 1/4] net: Register system page pool as an XDP memory model Toke Høiland-Jørgensen
2024-04-03 20:20 ` John Fastabend
2024-04-04 9:08 ` Alexander Lobakin
2024-02-20 21:03 ` [PATCH net-next v2 2/4] bpf: test_run: Use system page pool for XDP live frame mode Toke Høiland-Jørgensen
2024-02-21 14:48 ` Toke Høiland-Jørgensen
2024-04-04 11:23 ` Jesper Dangaard Brouer
2024-04-04 13:34 ` Toke Høiland-Jørgensen
2024-04-03 16:34 ` Alexander Lobakin
2024-04-03 20:39 ` John Fastabend [this message]
2024-04-04 11:43 ` Jesper Dangaard Brouer
2024-04-04 13:09 ` Alexander Lobakin
2024-02-20 21:03 ` [PATCH net-next v2 3/4] bpf: test_run: Fix cacheline alignment of live XDP frame data structures Toke Høiland-Jørgensen
2024-02-21 14:45 ` [PATCH net-next v2 0/4] Change BPF_TEST_RUN use the system page pool for live XDP frames Toke Høiland-Jørgensen
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