[Xen-devel] arm: network throughput decreases 5Mbps (Arndale Exynos5250)

[Sengul Thomas <thomas.sengul@xxxxxxxxx>]

Hello,

While I was doing some tests in Arndale board, the network (iperf)
throughput suddenly decreases to 5Mbps (from 100Mbps) out of nowhere.

This typically happens when I generate traffic using iperf (100Mbps)
while installing some packages using apt-get in dom0.
Whenever this behavior happens, I can not see any distinguishable logs
from any places.

After some debugging, I found that usb_hcd_irq handler
(linux/drivers/usb/core/hcd.c)
is not called and the pending requests are only handled by periodic
timer (100ms).
That is the reason of the sharp throughput reduction. I also checked
that the flag for
usb_hcd_irq is not disabled in Linux, and saw no reason for not
calling usb_hcd_irq.

This is quite a odd behavior since I can not see this happening when I
run native linux
on top of Arndale, so I guess it is somehow related to xen (maybe vgic
delivery).

I would like to know if there is any tracing or debugging helpers (for
vgic and evt_chn)
in Xen or Linux to see further what triggers this behavior.
I'm a bit tired of using printk all over the places :)


Here goes the branch that I'm using:
xen: git://xenbits.xen.org/people/julieng/xen-unstable.git
Dom0: git://xenbits.xen.org/people/julieng/linux-arm.git

Sincerely,
Thomas

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