netdev - Re: [PATCH RFC net-next 1/2] net: Reference bpf_redirect_info via task_struct on PREEMPT

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Message-ID: <20240222092228.4ACXUrvU@linutronix.de>
Date: Thu, 22 Feb 2024 10:22:28 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Jesper Dangaard Brouer <hawk@...nel.org>
Cc: Toke Høiland-Jørgensen <toke@...hat.com>,
	bpf@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH RFC net-next 1/2] net: Reference bpf_redirect_info via
 task_struct on PREEMPT_RT.

On 2024-02-20 16:32:08 [+0100], To Jesper Dangaard Brouer wrote:
> > 
> >  Ethtool(i40e2) stat:     15028585 (  15,028,585) <= tx-0.packets /sec
> >  Ethtool(i40e2) stat:     15028589 (  15,028,589) <= tx_packets /sec
> 
> -t1 in ixgbe
> Show adapter(s) (eth1) statistics (ONLY that changed!)
> Ethtool(eth1    ) stat:    107857263 (    107,857,263) <= tx_bytes /sec
> Ethtool(eth1    ) stat:    115047684 (    115,047,684) <= tx_bytes_nic /sec
> Ethtool(eth1    ) stat:      1797621 (      1,797,621) <= tx_packets /sec
> Ethtool(eth1    ) stat:      1797636 (      1,797,636) <= tx_pkts_nic /sec
> Ethtool(eth1    ) stat:    107857263 (    107,857,263) <= tx_queue_0_bytes /sec
> Ethtool(eth1    ) stat:      1797621 (      1,797,621) <= tx_queue_0_packets /sec
…
> while sending with ixgbe while running perf top on the box:
> | Samples: 621K of event 'cycles', 4000 Hz, Event count (approx.): 49979376685 lost: 0/0 drop: 0/0
> | Overhead  CPU  Command          Shared Object             Symbol
> |   31.98%  000  kpktgend_0       [kernel]                  [k] xas_find
> |    6.72%  000  kpktgend_0       [kernel]                  [k] pfn_to_dma_pte
> |    5.63%  000  kpktgend_0       [kernel]                  [k] ixgbe_xmit_frame_ring
> |    4.78%  000  kpktgend_0       [kernel]                  [k] dma_pte_clear_level
> |    3.16%  000  kpktgend_0       [kernel]                  [k] __iommu_dma_unmap

I disabled the iommu and I get to

Ethtool(eth1    ) stat:     14158562 (     14,158,562) <= tx_packets /sec
Ethtool(eth1    ) stat:     14158685 (     14,158,685) <= tx_pkts_nic /sec

looks like a small improvement… It is not your 15 but close. -t2 does
improve the situation. There is a warning from DMA mapping code but ;)

> > --Jesper

Sebastian