netdev - Re: [PATCH net-next v2 2/4] bpf: test_run: Use system page pool for XDP live frame mode

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Message-ID: <2746b1d9-2e1f-4e66-89ed-19949a189a92@intel.com>
Date: Wed, 3 Apr 2024 18:34:30 +0200
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Toke Høiland-Jørgensen <toke@...hat.com>
CC: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann
	<daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
	<martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu
	<song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, John Fastabend
	<john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, Stanislav Fomichev
	<sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	"David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
	Jesper Dangaard Brouer <hawk@...nel.org>, Eric Dumazet <edumazet@...gle.com>,
	Paolo Abeni <pabeni@...hat.com>, <bpf@...r.kernel.org>,
	<netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2 2/4] bpf: test_run: Use system page pool for
 XDP live frame mode

From: Toke Høiland-Jørgensen <toke@...hat.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@...el.com>
> Tested-by: Alexander Lobakin <aleksander.lobakin@...el.com>
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>

Hey,

What's the status of this series, now that the window is open?

Thanks,
Olek