Re: [ath9k-devel] Interrupt mitigation for USB Atheros dongles
On 2014-02-14 02:45, Dimosthenis Pediaditakis wrote:
Hi all,
I am using a capacity and available bandwidth measurement software that
compute estimates based on the gaps among packet trains/pairs.
For that reason I need to disable RX/TX interrupt mitigation for the
devices that I take the measurement form, because it introduces skew,
and renders unmeasurable the fast links ( 54Kbps).
The less latencies the drivers+kernel introduces, the better.
I have so far managed to disable all together the RX mitigation for
mini-PCIe devices by hard-coding the following line in
linux/drivers/net/wireless/ath/ath9k/ hw.c
ah-config.rx_intr_mitigation = false;
It seems to me that a better way to do this would be to drop your
fragile software based time measurement of rx interrupts, and instead
use the hardware timestamp (measured in microseconds).
While the above trick improves my results, it doesn't change the
behaviour of the Atheros-based USB WiFi dongles.
AFAIK my TP-Link TL-WN722N USB dongle uses the ath9k_htc driver, but I
haven't found anything relevant in the respective sources ( htc_*.{c, h} )
There is no interrupt mitigation here.
Apart from that, I suspect that the USB-net driver itself might also
introduce some fixed delays which affect the minimum time-spacing
measurement that my software can perceive at the receiver side.
USB in general adds too much latency for what you want to do.
Use hardware timestamps here as well.
- Felix
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Re: [ath9k-devel] Interrupt mitigation for USB Atheros dongles
Hm, do we have a sane way to get an unmolested RX timestamp?
like, is there any twiddle we can do to use the second TSF on Kiwi and
later and leave it free-running, so in STA mode we can get the RX
timestamps from said free-running clock, rather than the hostap BSS
adjusted TSF?
-a
On 14 February 2014 02:50, Felix Fietkau n...@openwrt.org wrote:
On 2014-02-14 02:45, Dimosthenis Pediaditakis wrote:
Hi all,
I am using a capacity and available bandwidth measurement software that
compute estimates based on the gaps among packet trains/pairs.
For that reason I need to disable RX/TX interrupt mitigation for the
devices that I take the measurement form, because it introduces skew,
and renders unmeasurable the fast links ( 54Kbps).
The less latencies the drivers+kernel introduces, the better.
I have so far managed to disable all together the RX mitigation for
mini-PCIe devices by hard-coding the following line in
linux/drivers/net/wireless/ath/ath9k/ hw.c
ah-config.rx_intr_mitigation = false;
It seems to me that a better way to do this would be to drop your
fragile software based time measurement of rx interrupts, and instead
use the hardware timestamp (measured in microseconds).
While the above trick improves my results, it doesn't change the
behaviour of the Atheros-based USB WiFi dongles.
AFAIK my TP-Link TL-WN722N USB dongle uses the ath9k_htc driver, but I
haven't found anything relevant in the respective sources ( htc_*.{c, h} )
There is no interrupt mitigation here.
Apart from that, I suspect that the USB-net driver itself might also
introduce some fixed delays which affect the minimum time-spacing
measurement that my software can perceive at the receiver side.
USB in general adds too much latency for what you want to do.
Use hardware timestamps here as well.
- Felix
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[ath9k-devel] Interrupt mitigation for USB Atheros dongles
Hi all,
I am using a capacity and available bandwidth measurement software that
compute estimates based on the gaps among packet trains/pairs.
For that reason I need to disable RX/TX interrupt mitigation for the
devices that I take the measurement form, because it introduces skew, and
renders unmeasurable the fast links ( 54Kbps).
The less latencies the drivers+kernel introduces, the better.
I have so far managed to disable all together the RX mitigation for
mini-PCIe devices by hard-coding the following line in
linux/drivers/net/wireless/ath/ath9k/ hw.c
ah-config.rx_intr_mitigation = false;
While the above trick improves my results, it doesn't change the behaviour
of the Atheros-based USB WiFi dongles.
AFAIK my TP-Link TL-WN722N USB dongle uses the ath9k_htc driver, but I
haven't found anything relevant in the respective sources ( htc_*.{c, h} )
Apart from that, I suspect that the USB-net driver itself might also
introduce some fixed delays which affect the minimum time-spacing
measurement that my software can perceive at the receiver side.
Here follow the details of my hardware:
https://wikidevi.com/wiki/TP-LINK_TL-WN722N
I am using linux kernel 3.11 at the moment, but I am flexible to switch to
a newer version.
Thank you in advance for your help,
Dimos
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