RE: Poor UDP performance using 2.6.21-rc5-rt5
From: David Sperry
Date: Mon Apr 02 2007 - 20:15:43 EST
> -----Original Message-----
> From: Ingo Molnar [mailto:mingo@xxxxxxx]
> Sent: Monday, April 02, 2007 3:05 PM
> To: dave_sperry@xxxxxxxx
> Cc: Dave Sperry; linux-rt-users@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx
> Subject: Re: Poor UDP performance using 2.6.21-rc5-rt5
>
>
> * dave_sperry@xxxxxxxx <dasperry@xxxxxxxxxxx> wrote:
>
> > The Intel NIC seems to behave better under RT
>
> yeah.
>
> > I think there is some kind of bad behavior happening in the Nvidia
> > driver with respect to softirq-net-tx and IRQ-8406.
>
> yes. Part of the problem is that the forcedeth.c driver does not fully
> support NAPI - today i've implemented those bits (see them below), based
> on your testcase. The other part is that the Intel NIC uses MSI, while
> foredeth uses fasteoi, correct? [you can see this in /proc/interrupts]
In my case forcedeth seems to be picking up MSI for eth2 & eth3
]$ cat /proc/interrupts
CPU0 CPU1
0: 110 0 IO-APIC-edge timer
1: 0 10 IO-APIC-edge i8042
8: 0 0 IO-APIC-edge rtc
9: 0 0 IO-APIC-fasteoi acpi
12: 0 124 IO-APIC-edge i8042
20: 0 0 IO-APIC-fasteoi libata
21: 4 7755 IO-APIC-fasteoi libata
22: 0 5570 IO-APIC-fasteoi ehci_hcd:usb2
23: 0 1 IO-APIC-fasteoi ohci_hcd:usb1, libata
8406: 7 15969 PCI-MSI-edge eth3
8407: 8 17249 PCI-MSI-edge eth2
8408: 0 131 PCI-MSI-edge eth1
8409: 0 85 PCI-MSI-edge eth0
NMI: 0 0
LOC: 201594 202389
ERR: 0
Could this be part of my problem?
The lspci for the device is:
00:08.0 Bridge: nVidia Corporation MCP55 Ethernet (rev a3)
Subsystem: Super Micro Computer Inc Unknown device 1611
Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr-
Stepping- SERR- FastB2B-
Status: Cap+ 66MHz+ UDF- FastB2B+ ParErr- DEVSEL=fast >TAbort-
<TAbort- <MAbort- >SERR- <PERR-
Latency: 0 (250ns min, 5000ns max)
Interrupt: pin A routed to IRQ 8407
Region 0: Memory at fe9ba000 (32-bit, non-prefetchable) [size=4K]
Region 1: I/O ports at a400 [size=8]
Region 2: Memory at fe9be800 (32-bit, non-prefetchable) [size=256]
Region 3: Memory at fe9be400 (32-bit, non-prefetchable) [size=16]
Capabilities: [44] Power Management version 2
Flags: PMEClk- DSI- D1+ D2+ AuxCurrent=0mA
PME(D0+,D1+,D2+,D3hot+,D3cold+)
Status: D0 PME-Enable+ DSel=0 DScale=0 PME-
Capabilities: [70] MSI-X: Enable- Mask- TabSize=8
Vector table: BAR=2 offset=00000000
PBA: BAR=3 offset=00000000
Capabilities: [50] Message Signalled Interrupts: 64bit+ Queue=0/3
Enable+
Address: 00000000fee0300c Data: 41b9
Capabilities: [6c] HyperTransport: MSI Mapping
00:09.0 Bridge: nVidia Corporation MCP55 Ethernet (rev a3)
Subsystem: Super Micro Computer Inc Unknown device 1611
Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr-
Stepping- SERR- FastB2B-
Status: Cap+ 66MHz+ UDF- FastB2B+ ParErr- DEVSEL=fast >TAbort-
<TAbort- <MAbort- >SERR- <PERR-
Latency: 0 (250ns min, 5000ns max)
Interrupt: pin A routed to IRQ 8406
Region 0: Memory at fe9b9000 (32-bit, non-prefetchable) [size=4K]
Region 1: I/O ports at a080 [size=8]
Region 2: Memory at fe9be000 (32-bit, non-prefetchable) [size=256]
Region 3: Memory at fe9b8c00 (32-bit, non-prefetchable) [size=16]
Capabilities: [44] Power Management version 2
Flags: PMEClk- DSI- D1+ D2+ AuxCurrent=0mA
PME(D0+,D1+,D2+,D3hot+,D3cold+)
Status: D0 PME-Enable+ DSel=0 DScale=0 PME-
Capabilities: [70] MSI-X: Enable- Mask- TabSize=8
Vector table: BAR=2 offset=00000000
PBA: BAR=3 offset=00000000
Capabilities: [50] Message Signalled Interrupts: 64bit+ Queue=0/3
Enable+
Address: 00000000fee0300c Data: 41c1
Capabilities: [6c] HyperTransport: MSI Mapping
>
> there are a few other things i'm working on to improve this. I've
> uploaded -rt9 which is the current state of affairs. Note that using
> -rt9 you'll likely only see IRQ-8406 overhead in the system, because
> i've added an optimization to do process the softirq-net-tx workload in
> the hardirq thread if the priority of the two is the same (which is the
> default behavior). But -rt9 is still work in progress that is not fully
> finished yet: in some cases i'm seeing 'fluctuating performance'
> problems on forcedeth that werent there before.
I tried -rt9 and saw some odd 'fluctuating performance'. I'll try it again
tomorrow when I am much closer to the box's power button.
Thanks again,
Dave
>
> Ingo
>
> --------------------->
> From: Ingo Molnar <mingo@xxxxxxx>
> Subject: [patch] forcedeth.c: improve NAPI handler
>
> another forcedeth.c thing: i noticed that its NAPI handler does not do
> tx-ring processing. The patch below implements this - tested on
> DESC_VER_2 hardware, with CONFIG_FORCEDETH_NAPI=y.
>
> Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
>
> Index: linux/drivers/net/forcedeth.c
> ===================================================================
> --- linux.orig/drivers/net/forcedeth.c
> +++ linux/drivers/net/forcedeth.c
> @@ -3118,9 +3118,17 @@ static int nv_napi_poll(struct net_devic
> int retcode;
>
> if (np->desc_ver == DESC_VER_1 || np->desc_ver == DESC_VER_2) {
> + spin_lock_irqsave(&np->lock, flags);
> + nv_tx_done(dev);
> + spin_unlock_irqrestore(&np->lock, flags);
> +
> pkts = nv_rx_process(dev, limit);
> retcode = nv_alloc_rx(dev);
> } else {
> + spin_lock_irqsave(&np->lock, flags);
> + nv_tx_done_optimized(dev, np->tx_ring_size);
> + spin_unlock_irqrestore(&np->lock, flags);
> +
> pkts = nv_rx_process_optimized(dev, limit);
> retcode = nv_alloc_rx_optimized(dev);
> }
-
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