On 08.08.2019 21:52, Holger Hoffstätte wrote: > On 8/8/19 8:17 PM, Heiner Kallweit wrote: >> On 08.08.2019 17:53, Holger Hoffstätte wrote: >>> 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 <hkallwe...@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.. >>> >> >> I was about to ask exactly that, whether you have TSO enabled. I don't know >> what >> can trigger the HW issue, it was just confirmed by Realtek that this chip >> version >> has a problem with TSO. So the logical conclusion is: test w/o TSO, ideally >> the >> linux-next version. > > So disabling TSO alone didn't work - it leads to reduced throughout (~70 MB/s > in iperf). > Instead I decided to backport 93681cd7d94f ("r8169: enable HW csum and TSO"), > which > wasn't easy due to cleanups/renamings of dependencies, but I managed to > backport > it and .. got the same problem of reduced throughout. wat?! > > After lots of trial & error I started disabling all offloads and finally found > that sg (Scatter-Gather) enabled alone - without TSO - will lead to the > throughput > drop. So the culprit seems 93681cd7d94f, which disabled TSO on my NIC, but > left > sg on by default. This weas repeatable - switch on sg, throughput drop; turn > it > off - smooth sailing, now with reduced buffers. > > I modified the relevant bits to disable tso & sg like this: > > /* RTL8168e-vl has a HW issue with TSO */ > if (tp->mac_version == RTL_GIGA_MAC_VER_34) { > + dev->vlan_features &= ~(NETIF_F_ALL_TSO|NETIF_F_SG); > + dev->hw_features &= ~(NETIF_F_ALL_TSO|NETIF_F_SG); > + dev->features &= ~(NETIF_F_ALL_TSO|NETIF_F_SG); > } > > This seems to work since it restores performance without sg/tso by default > and without any additional offloads, yet with xmit_more in the mix. > We'll see whether that is stable over the next few days, but I strongly > suspect it will be good and that the hiccups were due to xmit_more/TSO > interaction. > Thanks a lot for the analysis and testing. Then I'll submit the disabling of SG on RTL8168evl (on your behalf), independent of whether it fixes the timeout issue.
> thanks, > Holger > Heiner
