Re: [PATCH net-next] r8169: make use of xmit_more

["Holger Hoffstätte" <holger@applied-asynchrony.com>]

On 8/8/19 4:37 PM, Holger Hoffstätte wrote:
> 
> Hello Heiner -
> 
> On 7/28/19 11:25 AM, Heiner Kallweit wrote:
>> There was a previous attempt to use xmit_more, but the change had to be
>> reverted because under load sometimes a transmit timeout occurred [0].
>> Maybe this was caused by a missing memory barrier, the new attempt
>> keeps the memory barrier before the call to netif_stop_queue like it
>> is used by the driver as of today. The new attempt also changes the
>> order of some calls as suggested by Eric.
>>
>> [0] https://lkml.org/lkml/2019/2/10/39
>>
>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
> 
> I decided to take one for the team and merged this into my 5.2.x tree (just
> fixing up the path) and it has been working fine for the last 2 weeks in two
> machines..until today, when for the first time in forever some random NFS traffic
> made this old friend come out from under the couch:
> 
> [Aug 8 14:13] ------------[ cut here ]------------
> [  +0.000006] NETDEV WATCHDOG: eth0 (r8169): transmit queue 0 timed out
> [  +0.000021] WARNING: CPU: 3 PID: 0 at net/sched/sch_generic.c:442 dev_watchdog+0x21f/0x230
> [  +0.000001] Modules linked in: lz4 lz4_compress lz4_decompress nfsd auth_rpcgss oid_registry lockd grace sunrpc sch_fq_codel btrfs xor zstd_compress raid6_pq zstd_decompress bfq jitterentropy_rng nct6775 hwmon_vid coretemp hwmon x86_pkg_temp_thermal aesni_intel aes_x86_64 i915 glue_helper crypto_simd cryptd i2c_i801 intel_gtt i2c_algo_bit iosf_mbi drm_kms_helper syscopyarea usbhid sysfillrect r8169 sysimgblt fb_sys_fops realtek drm libphy drm_panel_orientation_quirks i2c_core video backlight mq_deadline
> [  +0.000026] CPU: 3 PID: 0 Comm: swapper/3 Not tainted 5.2.7 #1
> [  +0.000001] Hardware name: System manufacturer System Product Name/P8Z68-V LX, BIOS 4105 07/01/2013
> [  +0.000004] RIP: 0010:dev_watchdog+0x21f/0x230
> [  +0.000002] Code: 3b 00 75 ea eb ad 4c 89 ef c6 05 1c 45 bd 00 01 e8 66 35 fc ff 44 89 e1 4c 89 ee 48 c7 c7 e8 5e fc 81 48 89 c2 e8 90 df 92 ff <0f> 0b eb 8e 66 66 2e 0f 1f 84 00 00 00 00 00 66 90 66 66 66 66 90
> [  +0.000002] RSP: 0018:ffffc90000118e68 EFLAGS: 00010286
> [  +0.000002] RAX: 0000000000000000 RBX: ffff8887f7837600 RCX: 0000000000000303
> [  +0.000001] RDX: 0000000000000001 RSI: 0000000000000092 RDI: ffffffff827a488c
> [  +0.000001] RBP: ffff8887f9fbc440 R08: 0000000000000303 R09: 0000000000000003
> [  +0.000001] R10: 000000000001004c R11: 0000000000000001 R12: 0000000000000000
> [  +0.000009] R13: ffff8887f9fbc000 R14: ffffffff8173aa20 R15: dead000000000200
> [  +0.000001] FS:  0000000000000000(0000) GS:ffff8887ff580000(0000) knlGS:0000000000000000
> [  +0.000000] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  +0.000001] CR2: 00007f8d1c04d000 CR3: 0000000002209001 CR4: 00000000000606e0
> [  +0.000000] Call Trace:
> [  +0.000002]  <IRQ>
> [  +0.000005]  call_timer_fn+0x2b/0x120
> [  +0.000002]  expire_timers+0xa4/0x100
> [  +0.000001]  run_timer_softirq+0x8c/0x170
> [  +0.000002]  ? __hrtimer_run_queues+0x13a/0x290
> [  +0.000003]  ? sched_clock_cpu+0xe/0x130
> [  +0.000003]  __do_softirq+0xeb/0x2de
> [  +0.000003]  irq_exit+0x9d/0xe0
> [  +0.000002]  smp_apic_timer_interrupt+0x60/0x110
> [  +0.000003]  apic_timer_interrupt+0xf/0x20
> [  +0.000001]  </IRQ>
> [  +0.000003] RIP: 0010:cpuidle_enter_state+0xad/0x930
> [  +0.000001] Code: c5 66 66 66 66 90 31 ff e8 90 99 9e ff 80 7c 24 0b 00 74 12 9c 58 f6 c4 02 0f 85 39 08 00 00 31 ff e8 e7 26 a2 ff fb 45 85 e4 <0f> 88 34 02 00 00 49 63 cc 4c 2b 2c 24 48 8d 04 49 48 c1 e0 05 8b
> [  +0.000000] RSP: 0018:ffffc9000008be50 EFLAGS: 00000202 ORIG_RAX: ffffffffffffff13
> [  +0.000001] RAX: ffff8887ff5a9180 RBX: ffffffff822b6c40 RCX: 000000000000001f
> [  +0.000001] RDX: 0000000000000000 RSI: 0000000033087154 RDI: 0000000000000000
> [  +0.000001] RBP: ffff8887ff5b1310 R08: 000030d021fae397 R09: ffff8887ff59c8c0
> [  +0.000000] R10: ffff8887ff59c8c0 R11: 0000000000000006 R12: 0000000000000004
> [  +0.000001] R13: 000030d021fae397 R14: 0000000000000004 R15: ffff8887fc281600
> [  +0.000001]  cpuidle_enter+0x29/0x40
> [  +0.000002]  do_idle+0x1e5/0x280
> [  +0.000001]  cpu_startup_entry+0x19/0x20
> [  +0.000002]  start_secondary+0x186/0x1c0
> [  +0.000001]  secondary_startup_64+0xa4/0xb0
> [  +0.000001] ---[ end trace 99493c768580f4fd ]---
> 
> The device is:
> 
> Aug  7 23:19:09 tux kernel: libphy: r8169: probed
> Aug  7 23:19:09 tux kernel: r8169 0000:04:00.0 eth0: RTL8168evl/8111evl, c8:60:00:68:33:cc, XID 2c9, IRQ 36
> Aug  7 23:19:09 tux kernel: r8169 0000:04:00.0 eth0: jumbo features [frames: 9200 bytes, tx checksumming: ko]
> Aug  7 23:19:12 tux kernel: RTL8211E Gigabit Ethernet r8169-400:00: attached PHY driver [RTL8211E Gigabit Ethernet] (mii_bus:phy_addr=r8169-400:00, irq=IGNORE)
> Aug  7 23:19:13 tux kernel: r8169 0000:04:00.0 eth0: No native access to PCI extended config space, falling back to CSI
> 
> and using fq_codel, of course.
> 
> This cpuidle hiccup used to be completely gone without xmit_more and this was
> the first (and so far only) time since merging it (regardless of load).
> Also, while I'm using BMQ as CPU scheduler, that hasn't made a difference for
> this particular problem in the past (with MuQSS/PDS) either; way back when I had
> Eric's previous attempt(s) it also hiccupped with CFS.
> 
> Revert or wait for more reports when -next is merged in 5.4?

Another question/data point: I've had the whole basket of offloads activated:

   ethtool --offload eth0 rx on tx on gro on gso on sg on tso on

and this caused zero problems without the xmit_more patch. However I just saw
that net-next has a patch where TSO is disabled due to a known HW defect in
RTL8168evl, which is of course what I have. Could this be the reason for the
stall/hiccup when xmit_more has its fingers in the pie? I kind of know what
xmit_more does, just not how it could interact with a possibly broken TSO that
nevertheless seems to work fine otherwise..

thanks
Holger