Re: [Qemu-devel] [PATCH] rtl8139: honor RxOverflow flag in can_receive method

["Fernando Luis Vázquez Cao" <fernando@oss.ntt.co.jp>]

Hi Igor,

Thank you for the prompt reply. I really appreciate it.


(2012年01月31日 02:28), Igor Kovalenko wrote:
> 2012/1/30 Fernando Luis Vázquez Cao<fernando@oss.ntt.co.jp>:
>> Some drivers (Linux' 8139too among them) rely on the NIC injecting an interrupt
>> in the event of a receive buffer overflow and, accordingly, set the RxOverflow
>> bit in the interrupt mask. Unfortunately rtl8139's can_receive method ignores
>> the RxOverflow flag, which may lead to a situation where rtl8139 stops receiving
>> packets (can_receive returns 0) when the receive buffer becomes full.
>>
>> If the driver eventually read from the receive buffer or reset the card the
>> emulator could recover from this situation. However some implementations only
>> do this upon receiving an interrupt with either RxOK or RxOverflow set in the
>> ISR; interrupt that will never come because QEMU's flow control mechanisms would
>> prevent rtl8139 from receiving any packet.
>>
>> Letting packets go through when the overflow interrupt is enabled makes the
>> QEMU emulator compliant to the spec and solves the problem.
>>
>> This patch should fix a relatively common (in our experience) network stall
>> observed when running enterprise distros with rtl8139 as the NIC; in some cases
>> the 8139too device driver gets loaded and when under heavy load the network
>> eventually stops working.
> It would be great to see specific example to verify the issue.

Sure. In the gdb debug session included inline below you can see that 
after a
while RxBufPtr-RxBufAddr becomes too small to accommodate a MTU sized
packet and, because of the current can_receive logic, rtl8139 will stop 
receiving
packets from other QEMU VLAN clients.

> Otherwise the change looks great.

Could I have your "Acked-by"? By the way, whose tree should this patch 
go through?


----- gdb debug session

(gdb) p *(RTL8139State *) 0x144143a0
$3 = {phys = "TR\000bS:\000", mult = "\000\000\000\200\000\000\004@", 
TxStatus = {565346, 565346, 565346, 565346}, TxAddr = {899350528, 
899352064, 899353600,
     899355136}, RxBuf = 894697472, RxBufferSize = 32768, RxBufPtr = 0, 
RxBufAddr = 0, IntrStatus = 0, IntrMask = 49279, TxConfig = 2004878976, 
RxConfig = 63374,
   RxMissed = 0, CSCR = 832, Cfg9346 = 0 '\0', Config0 = 0 '\0', Config1 
= 12 '\f', Config3 = 1 '\001', Config4 = 0 '\0', Config5 = 0 '\0',
   clock_enabled = 1 '\001', bChipCmdState = 12 '\f', MultiIntr = 0, 
BasicModeCtrl = 4096, BasicModeStatus = 30765, NWayAdvert = 1505, 
NWayLPAR = 1505,
   NWayExpansion = 1, CpCmd = 0, TxThresh = 0 '\0', pci_dev = 
0x14414150, vc = 0x14414550, macaddr = "TR\000bS:", rtl8139_mmio_io_addr 
= 104, currTxDesc = 0,
   cplus_enabled = 0, currCPlusRxDesc = 0, currCPlusTxDesc = 0, 
RxRingAddrLO = 0, RxRingAddrHI = 0, eeprom = {contents = {33065, 4332, 
33081, 0, 0, 0, 0, 21076,
       25088, 14931, 0 <repeats 54 times>}, mode = 1, tick = 0, address 
= 9 '\t', input = 0, output = 0, eecs = 1 '\001', eesk = 0 '\0', eedi = 
0 '\0',
     eedo = 1 '\001'}, TCTR = 0, TimerInt = 0, TCTR_base = 0, 
tally_counters = {TxOk = 0, RxOk = 0, TxERR = 0, RxERR = 10, MissPkt = 
0, FAE = 0, Tx1Col = 0,
     TxMCol = 0, RxOkPhy = 1302, RxOkBrd = 2, RxOkMul = 10, TxAbt = 0, 
TxUndrn = 0}, cplus_txbuffer = 0x0, cplus_txbuffer_len = 0, 
cplus_txbuffer_offset = 0,
   timer = 0x0}
(gdb) c
Continuing.
[Thread 0x42c3a940 (LWP 2739) exited]
[New Thread 0x42c3a940 (LWP 2791)]

Program received signal SIGINT, Interrupt.
0x0000003a3a4cced2 in select () from /lib64/libc.so.6
(gdb) d
Delete all breakpoints? (y or n) y
(gdb)
(gdb) c
Continuing.

Program received signal SIGINT, Interrupt.
0x0000003a3a4cced2 in select () from /lib64/libc.so.6
(gdb) p *(RTL8139State *) 0x144143a0
$4 = {phys = "TR\000bS:\000", mult = "\000\000\000\200\000\000\004@", 
TxStatus = {565308, 565346, 565346, 565346}, TxAddr = {899350528, 
899352064, 899353600,
     899355136}, RxBuf = 894697472, RxBufferSize = 32768, RxBufPtr = 
22032, RxBufAddr = 20544, IntrStatus = 0, IntrMask = 49279, TxConfig = 
2004878976,
   RxConfig = 63374, RxMissed = 0, CSCR = 832, Cfg9346 = 0 '\0', Config0 
= 0 '\0', Config1 = 12 '\f', Config3 = 1 '\001', Config4 = 0 '\0', 
Config5 = 0 '\0',
   clock_enabled = 1 '\001', bChipCmdState = 12 '\f', MultiIntr = 0, 
BasicModeCtrl = 4096, BasicModeStatus = 30765, NWayAdvert = 1505, 
NWayLPAR = 1505,
   NWayExpansion = 1, CpCmd = 0, TxThresh = 0 '\0', pci_dev = 
0x14414150, vc = 0x14414550, macaddr = "TR\000bS:", rtl8139_mmio_io_addr 
= 104, currTxDesc = 1,
   cplus_enabled = 0, currCPlusRxDesc = 0, currCPlusTxDesc = 0, 
RxRingAddrLO = 0, RxRingAddrHI = 0, eeprom = {contents = {33065, 4332, 
33081, 0, 0, 0, 0, 21076,
       25088, 14931, 0 <repeats 54 times>}, mode = 1, tick = 0, address 
= 9 '\t', input = 0, output = 0, eecs = 1 '\001', eesk = 0 '\0', eedi = 
0 '\0',
     eedo = 1 '\001'}, TCTR = 0, TimerInt = 0, TCTR_base = 0, 
tally_counters = {TxOk = 0, RxOk = 0, TxERR = 0, RxERR = 10, MissPkt = 
0, FAE = 0, Tx1Col = 0,
     TxMCol = 0, RxOkPhy = 10277, RxOkBrd = 3, RxOkMul = 10, TxAbt = 0, 
TxUndrn = 0}, cplus_txbuffer = 0x0, cplus_txbuffer_len = 0, 
cplus_txbuffer_offset = 0,
   timer = 0x0}

-----


Thanks,
Fernando