netdev - Re: Decreasing time to get link up to below 3 s

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Date:   Fri, 31 May 2019 16:14:11 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Paul Menzel <pmenzel@...gen.mpg.de>
Cc:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Realtek linux nic maintainers <nic_swsd@...ltek.com>,
        intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Decreasing time to get link up to below 3 s

On Fri, May 31, 2019 at 03:19:20PM +0200, Paul Menzel wrote:
> Dear Linux folks,
> 
> 
> On several systems with different network devices and drivers (e1000e, r8169, tg3)
> it looks like getting the link up takes over three seconds.
> 
> ### e1000e ###
> 
> [    1.999678] e1000e: Intel(R) PRO/1000 Network Driver - 3.2.6-k
> [    2.000374] e1000e: Copyright(c) 1999 - 2015 Intel Corporation.
> [    2.001206] e1000e 0000:00:1f.6: Interrupt Throttling Rate (ints/sec) set to dynamic conservative mode
> [    2.412096] e1000e 0000:00:1f.6 0000:00:1f.6 (uninitialized): registered PHC clock
> [    2.495295] e1000e 0000:00:1f.6 eth0: (PCI Express:2.5GT/s:Width x1) 64:00:6a:2c:10:c1
> [    2.496204] e1000e 0000:00:1f.6 eth0: Intel(R) PRO/1000 Network Connection
> [    2.497024] e1000e 0000:00:1f.6 eth0: MAC: 12, PHY: 12, PBA No: FFFFFF-0FF
> [   15.614031] e1000e 0000:00:1f.6 net00: renamed from eth0
> [   18.679325] e1000e: net00 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: None

Hi Paul

All the Intel drivers do there own PHY handling, so i cannot speak for them.

> 
> ### r8169 ###
> 
> [   33.433103] r8169 0000:18:00.0: enabling device (0000 -> 0003)
> [   33.453834] libphy: r8169: probed
> [   33.456629] r8169 0000:18:00.0 eth0: RTL8168h/8111h, 30:9c:23:04:d6:98, XID 541, IRQ 52
> [   33.456631] r8169 0000:18:00.0 eth0: jumbo features [frames: 9200 bytes, tx checksumming: ko]
> [   33.607384] r8169 0000:18:00.0 enp24s0: renamed from eth0
> [   34.134035] Generic Realtek PHY r8169-1800:00: attached PHY driver [Generic Realtek PHY] (mii_bus:phy_addr=r8169-1800:00, irq=IGNORE)
> [   34.215244] r8169 0000:18:00.0 enp24s0: Link is Down
> [   37.822536] r8169 0000:18:00.0 enp24s0: Link is Up - 1Gbps/Full - flow control rx/tx

This is using the generic PHY framework and drivers.

You can see here irq=IGNORE. This implies interrupts are not being
used. So it will poll the PHY once per second. If you can get
interrupts working, you can save 1/2 second on average.


> ### tg3 ###
> 
> [    2.015604] tg3.c:v3.137 (May 11, 2014)
> [    2.025613] tg3 0000:04:00.0 eth0: Tigon3 [partno(BCM95762) rev 5762100] (PCI Express) MAC address 54:bf:64:70:a5:f9
> [    2.026955] tg3 0000:04:00.0 eth0: attached PHY is 5762C (10/100/1000Base-T Ethernet) (WireSpeed[1], EEE[1])
> [    2.028252] tg3 0000:04:00.0 eth0: RXcsums[1] LinkChgREG[0] MIirq[0] ASF[1] TSOcap[1]
> [    2.029462] tg3 0000:04:00.0 eth0: dma_rwctrl[00000001] dma_mask[64-bit]
> [    6.376904] tg3 0000:04:00.0 net00: renamed from eth0
> [   10.240411] tg3 0000:04:00.0 net00: Link is up at 1000 Mbps, full duplex
> [   10.240412] tg3 0000:04:00.0 net00: Flow control is on for TX and on for RX
> [   10.240413] tg3 0000:04:00.0 net00: EEE is disabled
> 

Another MAC driver which does not use the generic framework.

> If the time cannot be decreased, are there alternative strategies to get a link
> up as fast as possible? For fast boot systems, it’d be interesting if first
> a slower speed could be negotiated and later it would be changed.

You can use ethtool to set the modes it will offer for auto-neg. So
you could offer 10/half and see if that comes up faster.

ethtool -s eth0 advertise 0x001

But you are still going to have to wait the longer time when you
decide it is time to swap to the full bandwidth.

       Andrew