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Date: Mon, 6 Jul 2020 16:18:14 +0200
From: Kegl Rohit <keglrohit@...il.com>
To: Andy Duan <fugang.duan@....com>
Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [EXT] net: ethernet: freescale: fec: copybreak handling
throughput, dma_sync_* optimisations allowed?
So you would also say a single dma_sync_single_for_cpu is enough.
You are right it would be great if some mm expert could have a look at
it. If any corruption could happen.
diff --git a/drivers/net/ethernet/freescale/fec_main.c
b/drivers/net/ethernet/freescale/fec_main.c
index 2d0d313ee..acc04726f 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -1387,9 +1387,9 @@ static bool fec_enet_copybreak(struct net_device
*ndev, struct sk_buff **skb,
return false;
dma_sync_single_for_cpu(&fep->pdev->dev,
fec32_to_cpu(bdp->cbd_bufaddr),
- FEC_ENET_RX_FRSIZE - fep->rx_align,
+ length,
DMA_FROM_DEVICE);
if (!swap)
memcpy(new_skb->data, (*skb)->data, length);
else
@@ -1551,14 +1551,9 @@ fec_enet_rx_queue(struct net_device *ndev, int
budget, u16 queue_id)
vlan_tag);
napi_gro_receive(&fep->napi, skb);
- if (is_copybreak) {
- dma_sync_single_for_device(&fep->pdev->dev,
-
fec32_to_cpu(bdp->cbd_bufaddr),
- FEC_ENET_RX_FRSIZE
- fep->rx_align,
- DMA_FROM_DEVICE);
- } else {
+ if (!is_copybreak) {
rxq->rx_skbuff[index] = skb_new;
fec_enet_new_rxbdp(ndev, bdp, skb_new);
}
Testing is pretty complex because of multiple different contexts.
To test the whole rx chain throughput i decided to use UDP with 200
bytes payload.
Wireshark reports 242 bytes on wire, so copybreak is active (< 256 bytes).
I choose larger packets to reduce CPU load caused by the network stack / iperf3.
Smaller packets will benefit even more, but for this test the network
stack / iperf3 could become the bottleneck not the driver itself (e.g.
to test call skb_free instead of napi_gro_receive).
iperf missbehaved sometimes and caused a lot more CPU load, so using iperf3.
Kernelversion is Linux falcon 5.4.8-rt11-yocto-standard #59 SMP PREEMPT
Normaly our system has PREEMPT RT enabled. But I think to test
throughput PREEMPT is a better way to compare results.
NAPI and PREEMPT RT has even more contexts with the additional
threaded irq handler and therefore PREEMPT RT throughput is another
story.
stress -m 1 --vm-bytes 100M was used to simulate additional memory
load. Only one core to keep ressources free for iperf3.
###############################
# NOT PATCHED
###############################
-------------------------------
- NOT STRESSED
-------------------------------
user@ws:~/$ iperf3 -c 192.168.1.2 -u -l 200 -b 100M -t 10
Connecting to host 192.168.1.2, port 5201
[ 4] local 192.168.1.1 port 52032 connected to 192.168.1.2 port 5201
[ ID] Interval Transfer Bandwidth Total Datagrams
[ 4] 0.00-1.00 sec 8.06 MBytes 67.6 Mbits/sec 42279
[ 4] 1.00-2.00 sec 8.93 MBytes 74.9 Mbits/sec 46800
[ 4] 2.00-3.00 sec 8.92 MBytes 74.8 Mbits/sec 46771
[ 4] 3.00-4.00 sec 8.91 MBytes 74.7 Mbits/sec 46701
[ 4] 4.00-5.00 sec 8.92 MBytes 74.9 Mbits/sec 46792
[ 4] 5.00-6.00 sec 8.93 MBytes 74.9 Mbits/sec 46840
[ 4] 6.00-7.00 sec 8.90 MBytes 74.6 Mbits/sec 46636
[ 4] 7.00-8.00 sec 8.95 MBytes 75.1 Mbits/sec 46924
[ 4] 8.00-9.00 sec 8.91 MBytes 74.7 Mbits/sec 46716
[ 4] 9.00-10.00 sec 8.89 MBytes 74.5 Mbits/sec 46592
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Jitter
Lost/Total Datagrams
[ 4] 0.00-10.00 sec 88.3 MBytes 74.1 Mbits/sec 0.056 ms
123112/463051 (27%)
[ 4] Sent 463051 datagrams
[root@...6q ~]# iperf3 -s
Server listening on 5201
Accepted connection from 192.168.1.1, port 53394
[ 5] local 192.168.1.2 port 5201 connected to 192.168.1.1 port 43224
[ ID] Interval Transfer Bitrate Jitter
Lost/Total Datagrams
[ 5] 0.00-1.00 sec 5.56 MBytes 46.6 Mbits/sec 0.046 ms
5520/34650 (16%)
[ 5] 1.00-2.00 sec 6.40 MBytes 53.7 Mbits/sec 0.050 ms
13035/46576 (28%)
[ 5] 2.00-3.00 sec 6.40 MBytes 53.7 Mbits/sec 0.044 ms
13295/46854 (28%)
[ 5] 3.00-4.00 sec 6.26 MBytes 52.5 Mbits/sec 0.056 ms
13849/46692 (30%)
[ 5] 4.00-5.00 sec 6.31 MBytes 53.0 Mbits/sec 0.052 ms
13735/46833 (29%)
[ 5] 5.00-6.00 sec 6.32 MBytes 53.0 Mbits/sec 0.054 ms
13610/46761 (29%)
[ 5] 6.00-7.00 sec 6.32 MBytes 53.0 Mbits/sec 0.043 ms
13780/46931 (29%)
[ 5] 7.00-8.00 sec 6.33 MBytes 53.1 Mbits/sec 0.051 ms
13679/46848 (29%)
[ 5] 8.00-9.00 sec 6.33 MBytes 53.1 Mbits/sec 0.050 ms
13746/46912 (29%)
[ 5] 9.00-10.00 sec 6.33 MBytes 53.1 Mbits/sec 0.043 ms
13437/46626 (29%)
[ 5] 10.00-10.17 sec 1.04 MBytes 52.5 Mbits/sec 0.044 ms
2233/7684 (29%)
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Jitter
Lost/Total Datagrams
[ 5] 0.00-10.17 sec 63.6 MBytes 52.5 Mbits/sec 0.044 ms
129919/463367 (28%) receiver
[root@...6q ~]# mpstat -P ALL 4 1
Linux 5.4.8-rt11 03/17/00 _armv7l_ (4 CPU)
23:38:51 CPU %usr %nice %sys %iowait %irq %soft
%steal %guest %idle
23:38:55 all 2.49 0.00 19.96 0.00 0.00 25.45
0.00 0.00 52.10
23:38:55 0 0.00 0.00 0.25 0.00 0.00 99.75
0.00 0.00 0.00
23:38:55 1 1.54 0.00 11.54 0.00 0.00 0.00
0.00 0.00 86.92
23:38:55 2 1.27 0.00 5.85 0.00 0.00 0.00
0.00 0.00 92.88
23:38:55 3 7.24 0.00 63.31 0.00 0.00 0.00
0.00 0.00 29.46
=> ksoftirqd/0 @ 100%; iperf @ 94%
[root@...6q ~]# sar -I 60 1
00:13:32 INTR intr/s
00:13:33 60 0.00
00:13:34 60 0.00
00:13:35 60 0.00
00:13:36 60 0.00
=> 100% napi poll
-------------------------------
- STRESSED
- stress -m 1 --vm-bytes 100M &
-------------------------------
user@ws:~/$ iperf3 -c 192.168.1.2 -u -l 200 -b 100M -t 10
Connecting to host 192.168.1.2, port 5201
[ 4] local 192.168.1.1 port 52129 connected to 192.168.1.2 port 5201
[ ID] Interval Transfer Bandwidth Total Datagrams
[ 4] 0.00-1.00 sec 8.09 MBytes 67.8 Mbits/sec 42399
[ 4] 1.00-2.00 sec 8.88 MBytes 74.5 Mbits/sec 46552
[ 4] 2.00-3.00 sec 8.92 MBytes 74.8 Mbits/sec 46780
[ 4] 3.00-4.00 sec 8.91 MBytes 74.7 Mbits/sec 46688
[ 4] 4.00-5.00 sec 8.91 MBytes 74.7 Mbits/sec 46712
[ 4] 5.00-6.00 sec 8.91 MBytes 74.8 Mbits/sec 46724
[ 4] 6.00-7.00 sec 8.95 MBytes 75.0 Mbits/sec 46900
[ 4] 7.00-8.00 sec 8.95 MBytes 75.1 Mbits/sec 46928
[ 4] 8.00-9.00 sec 8.93 MBytes 74.9 Mbits/sec 46796
[ 4] 9.00-10.00 sec 8.91 MBytes 74.8 Mbits/sec 46732
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Jitter
Lost/Total Datagrams
[ 4] 0.00-10.00 sec 88.4 MBytes 74.1 Mbits/sec 0.067 ms
233989/463134 (51%)
[ 4] Sent 463134 datagrams
[root@...6q ~]# iperf3 -s
Server listening on 5201
Accepted connection from 192.168.1.1, port 57892
[ 5] local 192.168.1.2 port 5201 connected to 192.168.1.1 port 43729
[ ID] Interval Transfer Bitrate Jitter
Lost/Total Datagrams
[ 5] 0.00-1.00 sec 3.59 MBytes 30.1 Mbits/sec 0.071 ms
13027/31836 (41%)
[ 5] 1.00-2.00 sec 4.32 MBytes 36.2 Mbits/sec 0.075 ms
23690/46345 (51%)
[ 5] 2.00-3.00 sec 4.28 MBytes 35.9 Mbits/sec 0.040 ms
24879/47293 (53%)
[ 5] 3.00-4.00 sec 4.05 MBytes 34.0 Mbits/sec 0.055 ms
24430/45651 (54%)
[ 5] 4.00-5.00 sec 4.01 MBytes 33.6 Mbits/sec 0.130 ms
25200/46209 (55%)
[ 5] 5.00-6.00 sec 4.22 MBytes 35.4 Mbits/sec 0.052 ms
24777/46902 (53%)
[ 5] 6.00-7.00 sec 4.04 MBytes 33.9 Mbits/sec 0.057 ms
24452/45635 (54%)
[ 5] 7.00-8.00 sec 4.26 MBytes 35.7 Mbits/sec 0.063 ms
26530/48871 (54%)
[ 5] 8.00-9.00 sec 4.06 MBytes 34.1 Mbits/sec 0.061 ms
24293/45583 (53%)
[ 5] 9.00-10.00 sec 4.15 MBytes 34.8 Mbits/sec 0.155 ms
24752/46499 (53%)
[ 5] 10.00-10.25 sec 985 KBytes 32.5 Mbits/sec 0.069 ms
6246/11291 (55%)
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Jitter
Lost/Total Datagrams
[ 5] 0.00-10.25 sec 41.9 MBytes 34.3 Mbits/sec 0.069 ms
242276/462115 (52%) receiver
[root@...6q ~]# mpstat -P ALL 4 1
Linux 5.4.8-rt11 03/17/00 _armv7l_ (4 CPU)
23:43:12 CPU %usr %nice %sys %iowait %irq %soft
%steal %guest %idle
23:43:16 all 2.51 0.00 42.42 0.00 0.00 25.47
0.00 0.00 29.59
23:43:16 0 0.00 0.00 1.25 0.00 0.00 98.75
0.00 0.00 0.00
23:43:16 1 2.25 0.00 97.75 0.00 0.00 0.00
0.00 0.00 0.00
23:43:16 2 0.25 0.00 2.29 0.00 0.00 0.00
0.00 0.00 97.46
23:43:16 3 8.08 0.00 70.75 0.00 0.00 0.00
0.00 0.00 21.17
=> ksoftirqd/0 @ 100%; stress @ 100%; iperf3 @ 84%
[root@...6q ~]# sar -I 60 1
00:14:41 INTR intr/s
00:14:42 60 0.00
00:14:43 60 0.00
00:14:44 60 0.00
=> 100% napi poll
###############################
# PATCHED
###############################
-------------------------------
-NOT STRESSED
-------------------------------
user@ws:~/$ iperf3 -c 192.168.1.2 -u -l 200 -b 100M -t 10
Connecting to host 192.168.1.2, port 5201
[ 4] local 192.168.1.1 port 50177 connected to 192.168.1.2 port 5201
[ ID] Interval Transfer Bandwidth Total Datagrams
[ 4] 0.00-1.00 sec 8.08 MBytes 67.8 Mbits/sec 42373
[ 4] 1.00-2.00 sec 8.91 MBytes 74.7 Mbits/sec 46693
[ 4] 2.00-3.00 sec 8.93 MBytes 74.9 Mbits/sec 46803
[ 4] 3.00-4.00 sec 8.93 MBytes 74.9 Mbits/sec 46804
[ 4] 4.00-5.00 sec 8.93 MBytes 74.9 Mbits/sec 46804
[ 4] 5.00-6.00 sec 8.92 MBytes 74.8 Mbits/sec 46764
[ 4] 6.00-7.00 sec 8.95 MBytes 75.1 Mbits/sec 46944
[ 4] 7.00-8.00 sec 8.90 MBytes 74.7 Mbits/sec 46672
[ 4] 8.00-9.00 sec 8.91 MBytes 74.8 Mbits/sec 46732
[ 4] 9.00-10.00 sec 8.90 MBytes 74.7 Mbits/sec 46660
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Jitter
Lost/Total Datagrams
[ 4] 0.00-10.00 sec 88.4 MBytes 74.1 Mbits/sec 0.032 ms
16561/463165 (3.6%)
[ 4] Sent 463165 datagrams
[root@...6q ~]# iperf3 -s
Server listening on 5201
Accepted connection from 192.168.1.1, port 45012
[ 5] local 192.168.1.2 port 5201 connected to 192.168.1.1 port 50177
[ ID] Interval Transfer Bitrate Jitter
Lost/Total Datagrams
[ 5] 0.00-1.00 sec 7.36 MBytes 61.8 Mbits/sec 0.030 ms
1430/40038 (3.6%)
[ 5] 1.00-2.00 sec 8.60 MBytes 72.1 Mbits/sec 0.030 ms
1757/46850 (3.8%)
[ 5] 2.00-3.00 sec 8.61 MBytes 72.2 Mbits/sec 0.039 ms
1690/46809 (3.6%)
[ 5] 3.00-4.00 sec 8.61 MBytes 72.3 Mbits/sec 0.037 ms
1650/46812 (3.5%)
[ 5] 4.00-5.00 sec 8.59 MBytes 72.1 Mbits/sec 0.033 ms
1589/46651 (3.4%)
[ 5] 5.00-6.00 sec 8.60 MBytes 72.1 Mbits/sec 0.036 ms
1904/46967 (4.1%)
[ 5] 6.00-7.00 sec 8.61 MBytes 72.2 Mbits/sec 0.046 ms
1633/46766 (3.5%)
[ 5] 7.00-8.00 sec 8.60 MBytes 72.1 Mbits/sec 0.030 ms
1748/46818 (3.7%)
[ 5] 8.00-9.00 sec 8.61 MBytes 72.2 Mbits/sec 0.036 ms
1572/46707 (3.4%)
[ 5] 9.00-10.00 sec 8.61 MBytes 72.3 Mbits/sec 0.031 ms
1538/46703 (3.3%)
[ 5] 10.00-10.04 sec 389 KBytes 72.1 Mbits/sec 0.032 ms 50/2044 (2.4%)
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Jitter
Lost/Total Datagrams
[ 5] 0.00-10.04 sec 85.2 MBytes 71.1 Mbits/sec 0.032 ms
16561/463165 (3.6%) receiver
[root@...6q ~]# mpstat -P ALL 4 1
Linux 5.4.8-rt11-yocto-standard 03/17/00 _armv7l_ (4 CPU)
23:15:50 CPU %usr %nice %sys %iowait %irq %soft
%steal %guest %idle
23:15:54 all 3.06 0.00 26.11 0.00 0.00 11.09
0.00 0.00 59.74
23:15:54 0 0.00 0.00 0.00 0.00 0.00 86.44
0.00 0.00 13.56
23:15:54 1 10.25 0.00 89.50 0.00 0.00 0.25
0.00 0.00 0.00
23:15:54 2 0.00 0.00 0.00 0.00 0.00 0.00
0.00 0.00 100.00
23:15:54 3 0.00 0.00 0.00 0.00 0.00 0.00
0.00 0.00 100.00
=> ksoftirqd/* @ 0% CPU; iperf3 @ 100%
[root@...6q ~]# sar -I 60 1
23:56:10 INTR intr/s
23:56:11 60 12339.00
23:56:12 60 11476.00
=> irq load high
-------------------------------
- STRESSED
- stress -m 1 --vm-bytes 100M &
-------------------------------
user@ws:~/$ iperf3 -c 192.168.1.2 -u -l 200 -b 100M -t 10
Connecting to host 192.168.1.2, port 5201
[ 4] local 192.168.1.1 port 59042 connected to 192.168.1.2 port 5201
[ ID] Interval Transfer Bandwidth Total Datagrams
[ 4] 0.00-1.00 sec 7.92 MBytes 66.2 Mbits/sec 41527
[ 4] 1.00-2.00 sec 8.95 MBytes 75.4 Mbits/sec 46931
[ 4] 2.00-3.00 sec 8.95 MBytes 75.1 Mbits/sec 46923
[ 4] 3.00-4.00 sec 8.96 MBytes 75.2 Mbits/sec 46983
[ 4] 4.00-5.00 sec 8.96 MBytes 75.2 Mbits/sec 46999
[ 4] 5.00-6.00 sec 8.91 MBytes 74.5 Mbits/sec 46688
[ 4] 6.00-7.00 sec 8.93 MBytes 75.1 Mbits/sec 46824
[ 4] 7.00-8.00 sec 8.94 MBytes 75.0 Mbits/sec 46872
[ 4] 8.00-9.00 sec 8.91 MBytes 74.7 Mbits/sec 46700
[ 4] 9.00-10.00 sec 8.91 MBytes 74.8 Mbits/sec 46720
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Jitter
Lost/Total Datagrams
[ 4] 0.00-10.00 sec 88.3 MBytes 74.1 Mbits/sec 0.042 ms
70360/462955 (15%)
[ 4] Sent 462955 datagrams
[root@...6q ~]# iperf3 -s
Server listening on 5201
Accepted connection from 192.168.1.1, port 46306
[ 5] local 192.168.1.2 port 5201 connected to 192.168.1.1 port 59042
[ ID] Interval Transfer Bitrate Jitter
Lost/Total Datagrams
[ 5] 0.00-1.00 sec 6.54 MBytes 54.8 Mbits/sec 0.038 ms
5602/39871 (14%)
[ 5] 1.00-2.00 sec 7.51 MBytes 63.0 Mbits/sec 0.037 ms
6973/46362 (15%)
[ 5] 2.00-3.00 sec 7.54 MBytes 63.3 Mbits/sec 0.037 ms
7414/46966 (16%)
[ 5] 3.00-4.00 sec 7.56 MBytes 63.4 Mbits/sec 0.038 ms
7354/46984 (16%)
[ 5] 4.00-5.00 sec 7.60 MBytes 63.7 Mbits/sec 0.031 ms
7241/47069 (15%)
[ 5] 5.00-6.00 sec 7.58 MBytes 63.6 Mbits/sec 0.033 ms
7134/46865 (15%)
[ 5] 6.00-7.00 sec 7.56 MBytes 63.5 Mbits/sec 0.058 ms
6991/46649 (15%)
[ 5] 7.00-8.00 sec 7.57 MBytes 63.5 Mbits/sec 0.043 ms
7259/46933 (15%)
[ 5] 8.00-9.00 sec 7.56 MBytes 63.4 Mbits/sec 0.038 ms
7065/46721 (15%)
[ 5] 9.00-10.00 sec 7.55 MBytes 63.3 Mbits/sec 0.042 ms
7002/46588 (15%)
[ 5] 10.00-10.04 sec 317 KBytes 61.8 Mbits/sec 0.042 ms 325/1947 (17%)
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Jitter
Lost/Total Datagrams
[ 5] 0.00-10.04 sec 74.9 MBytes 62.6 Mbits/sec 0.042 ms
70360/462955 (15%) receiver
[root@...6q ~]# mpstat -P ALL 4 1
Linux 5.4.8-rt11-yocto-standard 03/17/00 _armv7l_ (4 CPU)
23:49:59 CPU %usr %nice %sys %iowait %irq %soft
%steal %guest %idle
23:50:03 all 3.21 0.00 47.27 0.00 0.00 25.02
0.00 0.00 24.51
23:50:03 0 0.00 0.00 0.50 0.00 0.00 99.50
0.00 0.00 0.00
23:50:03 1 0.00 0.00 0.26 0.00 0.00 0.00
0.00 0.00 99.74
23:50:03 2 9.50 0.00 90.50 0.00 0.00 0.00
0.00 0.00 0.00
23:50:03 3 3.01 0.00 96.99 0.00 0.00 0.00
0.00 0.00 0.00
=> ksoftirqd/0 @ 92%; stress @ 100%; iperf3 @ 100%
[root@...6q ~]# sar -I 60 1
23:57:08 60 505.00
23:57:09 60 748.00
23:57:10 60 416.00
=> irq load low => napi active but not all the time
===============================================================
As a result the patched system stressed with memory load has a higher
throughput than the unpatched system without memory stress.
The system could nearly keep up with the desktop sending @ 75MBit/s
(100MBit/s link) with i210 / igb.
I think IRQ/s could reach a new peak because of the faster napi_poll /
rx_queue execution times.
iperf, iperf3 is mainly to test throughput. Is there any tool which
checks for connection reliability (packet content, sequence, ...)?
On Thu, Jul 2, 2020 at 11:14 AM Andy Duan <fugang.duan@....com> wrote:
>
> From: Kegl Rohit <keglrohit@...il.com> Sent: Thursday, July 2, 2020 3:39 PM
> > On Thu, Jul 2, 2020 at 6:18 AM Andy Duan <fugang.duan@....com> wrote:
> > > That should ensure the whole area is not dirty.
> >
> > dma_sync_single_for_cpu() and dma_sync_single_for_device() can or must be
> > used in pairs?
> > So in this case it is really necessary to sync back the skb data buffer via
> > dma_sync_single_for_device? Even when the CPU does not change any bytes
> > in the skb data buffer / readonly like in this case.
>
> No, if the buffer is not modified, dma_sync_single_for_device() is not necessary.
>
> For some arm64 core, the dcache invalidate on A53 is flush + invalidate, once the buffer
> is modified, it will cause read back wrong data without dma_sync_single_for_device().
> And the driver also support Coldfire platforms, I am not family with the arch.
>
> From current analyze for arm/arm64, I also think dma_sync_single_for_device() is not
> necessary due to the buffer is not modified.
>
> Anyway, it still need to get other experts comment, and it need to do many test and stress test.
>
> > And there is no DMA_BIDIRECTIONAL mapping.
> >
> > I thought copybreak it is not about the next frame size. It is about the current
> > frame. And the actual length is known via the size field in the finished DMA
> > descriptor.
> > Or do you mean that the next received frame could be no copybreak frame.
> > 1. Rx copybreakable frame with sizeX < copybreak 2. copybreak
> > dma_sync_single_for_cpu(dmabuffer, sizeX) 3. copybreak alloc new_skb,
> > memcpy(new_skb, dmabuffer, sizeX) 4. copybreak
> > dma_sync_single_for_device(dmabuffer, sizeX) 5. Rx non copybreakable
> > frame with sizeY >= copybreak 4. dma_unmap_single(dmabuffer,
> > FEC_ENET_RX_FRSIZE - fep->rx_align) is called and can cause data corruption
> > because not all bytes were marked dirty even if nobody DMA & CPU touched
> > them?
>
> No CPU touch, it should be clean.
> >
> > > > I am new to the DMA API on ARM. Are these changes regarding cache
> > > > flushing,... allowed? These would increase the copybreak throughput
> > > > by reducing CPU load.
> > >
> > > To avoid FIFO overrun, it requires to ensure PHY pause frame is enabled.
> >
> > As the errata states this is also not always true, because the first xoff could
> > arrive too late. Pause frames/flow control is not really common and could
> > cause troubles with other random network components acting different or not
> > supporting pause frames correctly. For example the driver itself does enable
> > pause frames for Gigabit by default. But we have no Gigabit Phy so no
> > FEC_QUIRK_HAS_GBIT and therefore pause frames are not supported by the
> > driver as of now.
> >
> >
> > It looks like copybreak is implemented similar to e1000_main.c
> > e1000_copybreak().
> > There is only the real/needed packet length (length =
> > le16_to_cpu(rx_desc->length)) is synced via dma_sync_single_for_cpu and no
> > dma_sync_single_for_device.
> >
> > Here is a diff with the previous changes assuming that
> > dma_sync_single_for_device must be used to avoid any cache flush backs
> > even when no data was changed.
>
> Below change seems fine, can you collect some data before you send out
> the patch for review.
> - run iperf stress test to ensure the stability
> - collect the performance improvement data
>
> Thanks.
> >
> > diff --git a/drivers/net/ethernet/freescale/fec_main.c
> > b/drivers/net/ethernet/freescale/fec_main.c
> > index 2d0d313ee..464783c15 100644
> > --- a/drivers/net/ethernet/freescale/fec_main.c
> > +++ b/drivers/net/ethernet/freescale/fec_main.c
> > @@ -1387,9 +1387,9 @@ static bool fec_enet_copybreak(struct net_device
> > *ndev, struct sk_buff **skb,
> > return false;
> >
> > dma_sync_single_for_cpu(&fep->pdev->dev,
> > fec32_to_cpu(bdp->cbd_bufaddr),
> > - FEC_ENET_RX_FRSIZE - fep->rx_align,
> > + length,
> > DMA_FROM_DEVICE);
> > if (!swap)
> > memcpy(new_skb->data, (*skb)->data, length);
> > else
> > @@ -1413,8 +1413,9 @@ fec_enet_rx_queue(struct net_device *ndev, int
> > budget, u16 queue_id)
> > unsigned short status;
> > struct sk_buff *skb_new = NULL;
> > struct sk_buff *skb;
> > ushort pkt_len;
> > + ushort pkt_len_nofcs;
> > __u8 *data;
> > int pkt_received = 0;
> > struct bufdesc_ex *ebdp = NULL;
> > bool vlan_packet_rcvd = false;
> > @@ -1479,9 +1480,10 @@ fec_enet_rx_queue(struct net_device *ndev, int
> > budget, u16 queue_id)
> > /* The packet length includes FCS, but we don't want to
> > * include that when passing upstream as it messes up
> > * bridging applications.
> > */
> > - is_copybreak = fec_enet_copybreak(ndev, &skb, bdp,
> > pkt_len - 4,
> > + pkt_len_nofcs = pkt_len - 4;
> > + is_copybreak = fec_enet_copybreak(ndev, &skb, bdp,
> > pkt_len_nofcs,
> > need_swap);
> > if (!is_copybreak) {
> > skb_new = netdev_alloc_skb(ndev,
> > FEC_ENET_RX_FRSIZE);
> > if (unlikely(!skb_new)) { @@ -1554,9 +1556,9
> > @@ fec_enet_rx_queue(struct net_device *ndev, int budget, u16 queue_id)
> >
> > if (is_copybreak) {
> > dma_sync_single_for_device(&fep->pdev->dev,
> >
> > fec32_to_cpu(bdp->cbd_bufaddr),
> > -
> > FEC_ENET_RX_FRSIZE
> > - fep->rx_align,
> > +
> > pkt_len_nofcs,
> >
> > DMA_FROM_DEVICE);
> > } else {
> > rxq->rx_skbuff[index] = skb_new;
> > fec_enet_new_rxbdp(ndev, bdp, skb_new);
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