From: Harold Huang <baymaxhuang@gmail.com>
To: users@dpdk.org
Cc: jasowang@redhat.com, Maxime Coquelin <maxime.coquelin@redhat.com>,
Chenbo Xia <chenbo.xia@intel.com>
Subject: Question about the sndbuf of the tap interface with vhost-net
Date: Wed, 23 Feb 2022 21:13:56 +0800 [thread overview]
Message-ID: <CAHJXk3b9WhMb7CDHbO3ixGg23G1u7Y+guoLQLWkARgX6Ssrpow@mail.gmail.com> (raw)
I see in dpdk virtio-user driver, the TUNSETSNDBUF is initialized with
INT_MAX, see: https://github.com/DPDK/dpdk/blob/main/drivers/net/virtio/virtio_user/vhost_kernel_tap.c#L169
It is ok because tap driver uses it to support tx baching, see this
patch: https://github.com/torvalds/linux/commit/0a0be13b8fe2cac11da2063fb03f0f39359b3069
But in tun_xdp_one, napi is not supported and I want to user napi in
tun_get_user to enable gro. As I result, I change the sndbuf to a
value such as 212992 in /proc/sys/net/core/wmem_default. But the
performance tested by iperf is greatly degraded, from 4.5 Gbps to
750Gbps per flow. I see the the iperf server consume 100% cpu core,
which should be the bottleneck of the this test. The perf top result
of iperf server cpu core is as follows:
'''
Samples: 72 of event 'cycles', 4000 Hz, Event count (approx.):
22685278 lost: 0/0 drop: 0/0
Overhead Shared O Symbol
59.86% [kernel] [k] report_bug
20.66% [kernel] [k] module_find_bug
6.51% [kernel] [k] common_interrupt
2.82% [kernel] [k] __slab_free
1.48% [kernel] [k] copy_user_enhanced_fast_string
1.44% [kernel] [k] __skb_datagram_iter
1.42% [kernel] [k] notifier_call_chain
1.41% [kernel] [k] irq_work_run_list
1.41% [kernel] [k] update_irq_load_avg
1.41% [kernel] [k] task_tick_fair
1.41% [kernel] [k] cmp_ex_search
0.16% [kernel] [k] __ghes_peek_estatus.isra.12
0.02% [kernel] [k] acpi_os_read_memory
0.00% [kernel] [k] native_apic_mem_write
'''
I am not clear about the test result. Can we change the sndbuf size in
dpdk? Is any way to enable vhost_net to use napi without changing the
tun kernel driver?
next reply other threads:[~2022-02-23 13:14 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-23 13:13 Harold Huang [this message]
2022-02-23 13:46 ` Harold Huang
2022-02-24 3:23 ` Jason Wang
2022-02-24 4:19 ` Harold Huang
2022-02-24 4:36 ` Harold Huang
2022-02-24 4:39 ` Jason Wang
2022-02-24 7:31 ` Harold Huang
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