Anton Vorontsov wrote:
Hi all,
Down here few question regarding networking throughput, I would
appreciate any thoughts or ideas.
On the MPC8315E-RDB board (CPU at 400MHz, CSB at 133 MHz) I'm observing
relatively low TCP throughput using gianfar driver...
What is the "target" of the test - is it another of those boards, or
something else?
The maximum value I've seen with the current kernels is 142 Mb/s of TCP
and 354 Mb/s of UDP (NAPI and interrupts coalescing enabled):
[EMAIL PROTECTED]:~# netperf -l 10 -H 10.0.1.1 -t TCP_STREAM -- -m 32768 -s
157344 -S 157344
TCP STREAM TEST to 10.0.1.1
#Cpu utilization 0.10
Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. 10^6bits/sec
206848 212992 32768 10.00 142.40
[EMAIL PROTECTED]:~# netperf -l 10 -H 10.0.1.1 -t UDP_STREAM -- -m 32768 -s
157344 -S 157344
UDP UNIDIRECTIONAL SEND TEST to 10.0.1.1
#Cpu utilization 100.00
Socket Message Elapsed Messages
Size Size Time Okay Errors Throughput
bytes bytes secs # # 10^6bits/sec
212992 32768 10.00 13539 0 354.84
206848 10.00 13539 354.84
I have _got_ to make CPU utilization enabled by default one of these
days :) At least for mechanisms which don't require calibration.
Is this normal?
Does gianfar do TSO? If not, what happens when you tell UDP_STREAM to
send 1472 byte messages to bypass IP fragmentation?
While stock netperf won't report what the socket buffer size becomes
when you allow autotuning to rear its head, you can take the top of
trunk and enable the "omni" tests (./configure --enable-omni) and those
versions of *_STREAM etc can report what the socket buffer size was at
the beginning and at the end of the test. You can let the stack autotune
and see if anything changes there. You can do the same with stock
netperf, just it will only report the initial socket buffer sizes...
netperf running in loopback gives me 329 Mb/s of TCP throughput:
[EMAIL PROTECTED]:~# netperf -l 10 -H 127.0.0.1 -t TCP_STREAM -- -m 32768 -s
157344 -S 157344
TCP STREAM TEST to 127.0.0.1
#Cpu utilization 100.00
#Cpu utilization 100.00
Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. 10^6bits/sec
212992 212992 32768 10.00 329.60
May I consider this as a something that is close to the Linux'
theoretical maximum for this setup? Or this isn't reliable test?
I'm always leery of using a loopback number. It excercises both send
and receive at the same time, but without the driver. Also, lo tends to
have a much larger MTU than a "standard" NIC and if that NIC doesn't to
TSO and LRO that can be a big difference in the number of times up and
down the stack per KB transferred.
I can compare with teh MPC8377E-RDB (very similar board - exactly the same
ethernet phy, the same drivers are used, i.e. everything is the same from
the ethernet stand point), but running at 666 MHz, CSB at 333MHz:
|CPU MHz|BUS MHz|UDP Mb/s|TCP Mb/s|
------------------------------------------
MPC8377| 666| 333| 646| 264|
MPC8315| 400| 133| 354| 142|
------------------------------------------
RATIO | 1.6| 2.5| 1.8| 1.8|
It seems that things are really dependant on the CPU/CSB speed.
What is the nature of the DMA stream between the two tests? I find it
interesting that the TCP Mb/s went up by more than the CPU MHz and
wonder how much the Bus MHz came into play there - perhaps there were
more DMA's to setup or across a broader memory footprint for TCP than
for UDP.
I've tried to tune gianfar driver in various ways... and it gave
some positive results with this patch:
diff --git a/drivers/net/gianfar.h b/drivers/net/gianfar.h
index fd487be..b5943f9 100644
--- a/drivers/net/gianfar.h
+++ b/drivers/net/gianfar.h
@@ -123,8 +123,8 @@ extern const char gfar_driver_version[];
#define GFAR_10_TIME 25600
#define DEFAULT_TX_COALESCE 1
-#define DEFAULT_TXCOUNT 16
-#define DEFAULT_TXTIME 21
+#define DEFAULT_TXCOUNT 80
+#define DEFAULT_TXTIME 105
#define DEFAULT_RXTIME 21
No ethtool coalescing tuning support for gianfar?-)
Basically this raises the tx interrupts coalescing threshold (raising
it more didn't help, as well as didn't help raising rx thresholds).
Now:
[EMAIL PROTECTED]:~# netperf -l 3 -H 10.0.1.1 -t TCP_STREAM -- -m 32768 -s
157344 -S 157344
TCP STREAM TEST to 10.0.1.1
#Cpu utilization 100.00
Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. 10^6bits/sec
206848 212992 32768 3.00 163.04
That is +21 Mb/s (14% up). Not fantastic, but good anyway.
As expected, the latency increased too:
Before the patch:
--- 10.0.1.1 ping statistics ---
20 packets transmitted, 20 received, 0% packet loss, time 18997ms
rtt min/avg/max/mdev = 0.108/0.124/0.173/0.022 ms
After:
--- 10.0.1.1 ping statistics ---
22 packets transmitted, 22 received, 0% packet loss, time 20997ms
rtt min/avg/max/mdev = 0.158/0.167/0.182/0.004 ms
34% up... heh. Should we sacrifice the latency in favour of throughput?
Is 34% latency growth bad thing? What is worse, lose 21 Mb/s or 34% of
latency? ;-)
Well, I'm not always fond of that sort of trade-off:
ftp://ftp.cup.hp.com/dist/networking/briefs/
there should be a nic latency vs tput writeup there.
Thanks in advance,
p.s. Btw, the patch above helps even better on the on the -rt kernels,
since on the -rt kernels the throughput is near 100 Mb/s, with the
patch the throughput is close to 140 Mb/s.
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