netdev - Re: e1000 performance issue in 4 simultaneous links

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Message-ID: <4786615F.9060606@intel.com>
Date:	Thu, 10 Jan 2008 10:18:07 -0800
From:	"Kok, Auke" <auke-jan.h.kok@...el.com>
To:	Breno Leitao <leitao@...ux.vnet.ibm.com>
CC:	bhutchings@...arflare.com, NetDev <netdev@...r.kernel.org>
Subject: Re: e1000 performance issue in 4 simultaneous links

Breno Leitao wrote:
> On Thu, 2008-01-10 at 16:36 +0000, Ben Hutchings wrote:
>>> When I run netperf in just one interface, I get 940.95 * 10^6 bits/sec
>>> of transfer rate. If I run 4 netperf against 4 different interfaces, I
>>> get around 720 * 10^6 bits/sec.
>> <snip>
>>
>> I take it that's the average for individual interfaces, not the
>> aggregate?
> Right, each of these results are for individual interfaces. Otherwise,
> we'd have a huge problem. :-)
> 
>> This can be mitigated by interrupt moderation and NAPI
>> polling, jumbo frames (MTU >1500) and/or Large Receive Offload (LRO).
>> I don't think e1000 hardware does LRO, but the driver could presumably
>> be changed use Linux's software LRO.
> Without using these "features" and keeping the MTU as 1500, do you think
> we could get a better performance than this one?
> 
> I also tried to increase my interface MTU to 9000, but I am afraid that
> netperf only transmits packets with less than 1500. Still investigating.
> 
>> single CPU this can become a bottleneck.  Does the test system have
>> multiple CPUs?  Are IRQs for the multiple NICs balanced across
>> multiple CPUs?
> Yes, this machine has 8 ppc 1.9Ghz CPUs. And the IRQs are balanced
> across the CPUs, as I see in /proc/interrupts: 


which is wrong and hurts performance. you want your ethernet irq's to stick to a
CPU for long times to prevent cache thrash.

please disable the in-kernel irq balancing code and use the userspace `irqbalance`
daemon.

Gee I should put that in my signature, I already wrote that twice today :)

Auke

> 
> # cat /proc/interrupts 
>            CPU0       CPU1       CPU2       CPU3       CPU4       CPU5       CPU6       CPU7       
>  16:        940        760       1047        904        993        777        975        813   XICS      Level     IPI
>  18:          4          3          4          1          3          6          8          3   XICS      Level     hvc_console
>  19:          0          0          0          0          0          0          0          0   XICS      Level     RAS_EPOW
> 273:      10728      10850      10937      10833      10884      10788      10868      10776   XICS      Level     eth4
> 275:          0          0          0          0          0          0          0          0   XICS      Level     ehci_hcd:usb1, ohci_hcd:usb2, ohci_hcd:usb3
> 277:     234933     230275     229770     234048     235906     229858     229975     233859   XICS      Level     eth6
> 278:     266225     267606     262844     265985     268789     266869     263110     267422   XICS      Level     eth7
> 279:        893        919        857        909        867        917        894        881   XICS      Level     eth0
> 305:     439246     439117     438495     436072     438053     440111     438973     438951   XICS      Level     eth0 Neterion Xframe II 10GbE network adapter
> 321:       3268       3088       3143       3113       3305       2982       3326       3084   XICS      Level     ipr
> 323:     268030     273207     269710     271338     270306     273258     270872     273281   XICS      Level     eth16
> 324:     215012     221102     219494     216732     216531     220460     219718     218654   XICS      Level     eth17
> 325:       7103       3580       7246       3475       7132       3394       7258       3435   XICS      Level     pata_pdc2027x
> BAD:       4216
> 
> Thanks,
> 

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