netdev - Re: [PATCH v10 07/12] net/mlx4_en: add page recycle to prepare rx ring for tx support

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Date:	Tue, 19 Jul 2016 14:49:37 -0700
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Brenden Blanco <bblanco@...mgrid.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Saeed Mahameed <saeedm@....mellanox.co.il>,
	Martin KaFai Lau <kafai@...com>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Ari Saha <as754m@....com>, Or Gerlitz <gerlitz.or@...il.com>,
	john.fastabend@...il.com, hannes@...essinduktion.org,
	Thomas Graf <tgraf@...g.ch>, Tom Herbert <tom@...bertland.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Tariq Toukan <ttoukan.linux@...il.com>
Subject: Re: [PATCH v10 07/12] net/mlx4_en: add page recycle to prepare rx
 ring for tx support

On Tue, Jul 19, 2016 at 12:16:52PM -0700, Brenden Blanco wrote:
> The mlx4 driver by default allocates order-3 pages for the ring to
> consume in multiple fragments. When the device has an xdp program, this
> behavior will prevent tx actions since the page must be re-mapped in
> TODEVICE mode, which cannot be done if the page is still shared.
> 
> Start by making the allocator configurable based on whether xdp is
> running, such that order-0 pages are always used and never shared.
> 
> Since this will stress the page allocator, add a simple page cache to
> each rx ring. Pages in the cache are left dma-mapped, and in drop-only
> stress tests the page allocator is eliminated from the perf report.
> 
> Note that setting an xdp program will now require the rings to be
> reconfigured.
> 
> Before:
>  26.91%  ksoftirqd/0  [mlx4_en]         [k] mlx4_en_process_rx_cq
>  17.88%  ksoftirqd/0  [mlx4_en]         [k] mlx4_en_alloc_frags
>   6.00%  ksoftirqd/0  [mlx4_en]         [k] mlx4_en_free_frag
>   4.49%  ksoftirqd/0  [kernel.vmlinux]  [k] get_page_from_freelist
>   3.21%  swapper      [kernel.vmlinux]  [k] intel_idle
>   2.73%  ksoftirqd/0  [kernel.vmlinux]  [k] bpf_map_lookup_elem
>   2.57%  swapper      [mlx4_en]         [k] mlx4_en_process_rx_cq
> 
> After:
>  31.72%  swapper      [kernel.vmlinux]       [k] intel_idle
>   8.79%  swapper      [mlx4_en]              [k] mlx4_en_process_rx_cq
>   7.54%  swapper      [kernel.vmlinux]       [k] poll_idle
>   6.36%  swapper      [mlx4_core]            [k] mlx4_eq_int
>   4.21%  swapper      [kernel.vmlinux]       [k] tasklet_action
>   4.03%  swapper      [kernel.vmlinux]       [k] cpuidle_enter_state
>   3.43%  swapper      [mlx4_en]              [k] mlx4_en_prepare_rx_desc
>   2.18%  swapper      [kernel.vmlinux]       [k] native_irq_return_iret
>   1.37%  swapper      [kernel.vmlinux]       [k] menu_select
>   1.09%  swapper      [kernel.vmlinux]       [k] bpf_map_lookup_elem
> 
> Signed-off-by: Brenden Blanco <bblanco@...mgrid.com>
...
> +#define MLX4_EN_CACHE_SIZE (2 * NAPI_POLL_WEIGHT)
> +struct mlx4_en_page_cache {
> +	u32 index;
> +	struct mlx4_en_rx_alloc buf[MLX4_EN_CACHE_SIZE];
> +};

amazing that this tiny recycling pool makes such a huge difference.
Acked-by: Alexei Starovoitov <ast@...nel.org>