From: "Samudrala, Sridhar" <sridhar.samudrala@intel.com>
To: "Alexei Starovoitov" <alexei.starovoitov@gmail.com>,
"Toke Høiland-Jørgensen" <toke@redhat.com>
Cc: "Jakub Kicinski" <jakub.kicinski@netronome.com>,
"Karlsson, Magnus" <magnus.karlsson@intel.com>,
"Björn Töpel" <bjorn.topel@intel.com>,
Netdev <netdev@vger.kernel.org>,
"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
intel-wired-lan <intel-wired-lan@lists.osuosl.org>,
"Fijalkowski, Maciej" <maciej.fijalkowski@intel.com>,
"Herbert, Tom" <tom.herbert@intel.com>
Subject: Re: FW: [PATCH bpf-next 2/4] xsk: allow AF_XDP sockets to receive packets directly from a queue
Date: Fri, 18 Oct 2019 17:45:26 -0700 [thread overview]
Message-ID: <6f281517-3785-ce46-65de-e2f78576783b@intel.com> (raw)
In-Reply-To: <20191019001449.fk3gnhih4nx724pm@ast-mbp>
On 10/18/2019 5:14 PM, Alexei Starovoitov wrote:
> On Fri, Oct 18, 2019 at 11:40:07AM -0700, Samudrala, Sridhar wrote:
>>
>> Perf report for "AF_XDP default rxdrop" with patched kernel - mitigations ON
>> ==========================================================================
>> Samples: 44K of event 'cycles', Event count (approx.): 38532389541
>> Overhead Command Shared Object Symbol
>> 15.31% ksoftirqd/28 [i40e] [k] i40e_clean_rx_irq_zc
>> 10.50% ksoftirqd/28 bpf_prog_80b55d8a76303785 [k] bpf_prog_80b55d8a76303785
>> 9.48% xdpsock [i40e] [k] i40e_clean_rx_irq_zc
>> 8.62% xdpsock xdpsock [.] main
>> 7.11% ksoftirqd/28 [kernel.vmlinux] [k] xsk_rcv
>> 5.81% ksoftirqd/28 [kernel.vmlinux] [k] xdp_do_redirect
>> 4.46% xdpsock bpf_prog_80b55d8a76303785 [k] bpf_prog_80b55d8a76303785
>> 3.83% xdpsock [kernel.vmlinux] [k] xsk_rcv
>
> why everything is duplicated?
> Same code runs in different tasks ?
Yes. looks like these functions run from both the app(xdpsock) context and ksoftirqd context.
>
>> 2.81% ksoftirqd/28 [kernel.vmlinux] [k] bpf_xdp_redirect_map
>> 2.78% ksoftirqd/28 [kernel.vmlinux] [k] xsk_map_lookup_elem
>> 2.44% xdpsock [kernel.vmlinux] [k] xdp_do_redirect
>> 2.19% ksoftirqd/28 [kernel.vmlinux] [k] __xsk_map_redirect
>> 1.62% ksoftirqd/28 [kernel.vmlinux] [k] xsk_umem_peek_addr
>> 1.57% xdpsock [kernel.vmlinux] [k] xsk_umem_peek_addr
>> 1.32% ksoftirqd/28 [kernel.vmlinux] [k] dma_direct_sync_single_for_cpu
>> 1.28% xdpsock [kernel.vmlinux] [k] bpf_xdp_redirect_map
>> 1.15% xdpsock [kernel.vmlinux] [k] dma_direct_sync_single_for_device
>> 1.12% xdpsock [kernel.vmlinux] [k] xsk_map_lookup_elem
>> 1.06% xdpsock [kernel.vmlinux] [k] __xsk_map_redirect
>> 0.94% ksoftirqd/28 [kernel.vmlinux] [k] dma_direct_sync_single_for_device
>> 0.75% ksoftirqd/28 [kernel.vmlinux] [k] __x86_indirect_thunk_rax
>> 0.66% ksoftirqd/28 [i40e] [k] i40e_clean_programming_status
>> 0.64% ksoftirqd/28 [kernel.vmlinux] [k] net_rx_action
>> 0.64% swapper [kernel.vmlinux] [k] intel_idle
>> 0.62% ksoftirqd/28 [i40e] [k] i40e_napi_poll
>> 0.57% xdpsock [kernel.vmlinux] [k] dma_direct_sync_single_for_cpu
>>
>> Perf report for "AF_XDP direct rxdrop" with patched kernel - mitigations ON
>> ==========================================================================
>> Samples: 46K of event 'cycles', Event count (approx.): 38387018585
>> Overhead Command Shared Object Symbol
>> 21.94% ksoftirqd/28 [i40e] [k] i40e_clean_rx_irq_zc
>> 14.36% xdpsock xdpsock [.] main
>> 11.53% ksoftirqd/28 [kernel.vmlinux] [k] xsk_rcv
>> 11.32% xdpsock [i40e] [k] i40e_clean_rx_irq_zc
>> 4.02% xdpsock [kernel.vmlinux] [k] xsk_rcv
>> 2.91% ksoftirqd/28 [kernel.vmlinux] [k] xdp_do_redirect
>> 2.45% ksoftirqd/28 [kernel.vmlinux] [k] xsk_umem_peek_addr
>> 2.19% xdpsock [kernel.vmlinux] [k] xsk_umem_peek_addr
>> 2.08% ksoftirqd/28 [kernel.vmlinux] [k] bpf_direct_xsk
>> 2.07% ksoftirqd/28 [kernel.vmlinux] [k] dma_direct_sync_single_for_cpu
>> 1.53% ksoftirqd/28 [kernel.vmlinux] [k] dma_direct_sync_single_for_device
>> 1.39% xdpsock [kernel.vmlinux] [k] dma_direct_sync_single_for_device
>> 1.22% ksoftirqd/28 [kernel.vmlinux] [k] xdp_get_xsk_from_qid
>> 1.12% ksoftirqd/28 [i40e] [k] i40e_clean_programming_status
>> 0.96% ksoftirqd/28 [i40e] [k] i40e_napi_poll
>> 0.95% ksoftirqd/28 [kernel.vmlinux] [k] net_rx_action
>> 0.89% xdpsock [kernel.vmlinux] [k] xdp_do_redirect
>> 0.83% swapper [i40e] [k] i40e_clean_rx_irq_zc
>> 0.70% swapper [kernel.vmlinux] [k] intel_idle
>> 0.66% xdpsock [kernel.vmlinux] [k] dma_direct_sync_single_for_cpu
>> 0.60% xdpsock [kernel.vmlinux] [k] bpf_direct_xsk
>> 0.50% ksoftirqd/28 [kernel.vmlinux] [k] xsk_umem_discard_addr
>>
>> Based on the perf reports comparing AF_XDP default and direct rxdrop, we can say that
>> AF_XDP direct rxdrop codepath is avoiding the overhead of going through these functions
>> bpf_prog_xxx
>> bpf_xdp_redirect_map
>> xsk_map_lookup_elem
>> __xsk_map_redirect
>> With AF_XDP direct, xsk_rcv() is directly called via bpf_direct_xsk() in xdp_do_redirect()
>
> I don't think you're identifying the overhead correctly.
> xsk_map_lookup_elem is 1%
> but bpf_xdp_redirect_map() suppose to call __xsk_map_lookup_elem()
> which is a different function:
> ffffffff81493fe0 T __xsk_map_lookup_elem
> ffffffff81492e80 t xsk_map_lookup_elem
>
> 10% for bpf_prog_80b55d8a76303785 is huge.
> It's the actual code of the program _without_ any helpers.
> How does the program actually look?
It is the xdp program that is loaded via xsk_load_xdp_prog() in tools/lib/bpf/xsk.c
https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/tools/lib/bpf/xsk.c#n268
In the archives, i see that Toke had some comments, but somehow i didn't get his email in
my inbox.
> Performance Results
> ===================
> Only 1 core is used in all these testcases as the app and the queue irq are pinned to the same core.
>
> ----------------------------------------------------------------------------------
> mitigations ON mitigations OFF
> Testcase ----------------------------------------------------------
> no patches with patches no patches with patches
> ----------------------------------------------------------------------------------
> AF_XDP default rxdrop X X Y Y
> Is this really exactly the same with and without patches? You're adding
> an extra check to xdp_do_redirect(); are you really saying that the
> impact of that is zero?
Yes. I didn't see any impact. The variation is within +/- < 1%
I could use static_key even for that check in xdp_do_redirect() if required.
-Sridhar
next prev parent reply other threads:[~2019-10-19 0:47 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-08 6:16 [PATCH bpf-next 0/4] Enable direct receive on AF_XDP sockets Sridhar Samudrala
2019-10-08 6:16 ` [PATCH bpf-next 1/4] bpf: introduce bpf_get_prog_id and bpf_set_prog_id helper functions Sridhar Samudrala
2019-10-08 6:16 ` [PATCH bpf-next 2/4] xsk: allow AF_XDP sockets to receive packets directly from a queue Sridhar Samudrala
2019-10-08 6:58 ` Toke Høiland-Jørgensen
2019-10-08 8:47 ` Björn Töpel
2019-10-08 8:48 ` Björn Töpel
2019-10-08 9:04 ` Toke Høiland-Jørgensen
2019-10-08 8:05 ` Björn Töpel
2019-10-09 16:32 ` Samudrala, Sridhar
2019-10-09 1:20 ` Alexei Starovoitov
[not found] ` <3ED8E928C4210A4289A677D2FEB48235140134CE@fmsmsx111.amr.corp.intel.com>
2019-10-09 16:53 ` FW: " Samudrala, Sridhar
2019-10-09 17:17 ` Alexei Starovoitov
2019-10-09 19:12 ` Samudrala, Sridhar
2019-10-10 1:06 ` Alexei Starovoitov
2019-10-18 18:40 ` Samudrala, Sridhar
2019-10-18 19:22 ` Toke Høiland-Jørgensen
2019-10-19 0:14 ` Alexei Starovoitov
2019-10-19 0:45 ` Samudrala, Sridhar [this message]
2019-10-19 2:25 ` Alexei Starovoitov
2019-10-20 10:14 ` Toke Høiland-Jørgensen
2019-10-20 17:12 ` [Intel-wired-lan] " Björn Töpel
2019-10-21 20:10 ` Samudrala, Sridhar
2019-10-21 22:34 ` Alexei Starovoitov
2019-10-22 19:06 ` Samudrala, Sridhar
2019-10-23 17:42 ` Alexei Starovoitov
2019-10-24 18:12 ` Samudrala, Sridhar
2019-10-25 7:42 ` Björn Töpel
2019-10-31 22:38 ` Samudrala, Sridhar
2019-10-31 23:15 ` Alexei Starovoitov
2019-11-01 0:21 ` Jakub Kicinski
2019-11-01 18:31 ` Samudrala, Sridhar
2019-11-04 2:08 ` dan
2019-10-25 9:07 ` Björn Töpel
2019-10-08 6:16 ` [PATCH bpf-next 3/4] libbpf: handle AF_XDP sockets created with XDP_DIRECT bind flag Sridhar Samudrala
2019-10-08 8:05 ` Björn Töpel
2019-10-08 6:16 ` [PATCH bpf-next 4/4] xdpsock: add an option to create AF_XDP sockets in XDP_DIRECT mode Sridhar Samudrala
2019-10-08 8:05 ` Björn Töpel
2019-10-08 8:05 ` [PATCH bpf-next 0/4] Enable direct receive on AF_XDP sockets Björn Töpel
2019-10-09 16:19 ` Samudrala, Sridhar
2019-10-09 0:49 ` Jakub Kicinski
2019-10-09 6:29 ` Samudrala, Sridhar
2019-10-09 16:53 ` Jakub Kicinski
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