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Re: [Xen-devel] Xen & I/O in clusters - problems! New Information

To: Xen Virtual Machine Monitor <xen-devel@xxxxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Xen & I/O in clusters - problems! New Information
From: Rune Johan Andresen <runejoha@xxxxxxxxxxx>
Date: Fri, 22 Oct 2004 18:36:54 +0200
Cc: Håvard Bjerke <Havard.Bjerke@xxxxxxxxxxx>
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We tried to compile xen0 with CONFIG_E1000_NAPI = y and got the samre results between
two xen dom0 nodes. I am not sure if these interrupts tells anything:

Native Linux:


 CPU0
  0:   87290435          XT-PIC  timer
  1:          2          XT-PIC  keyboard
  2:          0          XT-PIC  cascade
  3:    7668994          XT-PIC  eth0
  7:          0          XT-PIC  ehci-hcd
  8:          1          XT-PIC  rtc
 10:          3          XT-PIC  usb-uhci
 11:     332088          XT-PIC  aic7xxx, aic7xxx, usb-uhci
 14:          1          XT-PIC  ide0
 15:          0          XT-PIC  libata
NMI:          0
ERR:          0


Xen Dom0:

          CPU0
  1:          2        Phys-irq  keyboard
 14:          3        Phys-irq  ide0
 18:     954304        Phys-irq  eth0
 24:       7313        Phys-irq  aic7xxx
 25:         30        Phys-irq  aic7xxx
128:          1     Dynamic-irq  misdirect
129:          0     Dynamic-irq  ctrl-if
130:     241914     Dynamic-irq  timer
131:          0     Dynamic-irq  timer_dbg, net-be-dbg
132:          0     Dynamic-irq  console
NMI:          0
ERR:          0

If you can see anything which is not normal behavior of xen please
tell us :)

Cheers,
Rune


On Oct 21, 2004, at 10:24 PM, Ian Pratt wrote:


Between two Xen dom0 domains (between two physical computers in the
cluster) we got these strange results:
(We use ttcp socketbuffsize, 10^4 -> 10^6)

Kernel 2.6:
Xen Dom0 -> Xen Dom0: ca. 80 000 KB/s (?)

Native Linux:
Native Linux -> Native Linux: ca. 114 000 KB/s

What is new and strage is that Xen Dom0 use about 60% of the CPU when
transfering or receiving, while
Native Linux ony use 6-7%(!) It seems like we have a problem with the
DMA here(?). We use Xen 2.0,
Gigabit ethernet.

dom0 to dom0 performance really shouldn't be any difference from
native. It certainly isn't on any of our machines.

The only thing I can think of is that something stupid might be
happening with interrupts on your machines. Can you compare the
rate that the relevant interrupts are going up in
/proc/interrupts between xenLinux and native.

There's no interrupt sharing or anything daft like that going on?
Are you using NAPI on the native e1000 linux driver?


Ian



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