NFS stalling at a certain transfer limit

Elf

Storybook
Feb 4, 2019
567
155
43
Today I was running into a problem with NFS stalling out on a copy from a remote machine to IRIX. NFS worked generally, but while copying the file it would always stall out at exactly the same place. The place it would stall was different for different files, but always completely repeatable for the same file and much greater than the MTU (e.g. one file would always stall out at 44 mbyte).

The client / receiving side was IRIX is 6.5.19 and the machine is a Challenge S on a 10mbit half-duplex ethernet AUI transceiver, and the server / sending side was FreeBSD 13.0 on 1gbit full duplex Ethernet.

What this looked like on the network (from the sender's perspective) was normal NFS traffic with no retries up until the point of the stall, e.g.:
Code:
36996    43.296638    172.18.0.5    172.18.0.3    NFS    178    V3 READ Call (Reply In 37008), FH: 0xc071e444 Offset: 46612480 Len: 16384
36997    43.296701    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=0, ID=133e) [Reassembled in #37008]
36998    43.296704    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=1480, ID=133e) [Reassembled in #37008]
36999    43.296706    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=2960, ID=133e) [Reassembled in #37008]
37000    43.296708    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=4440, ID=133e) [Reassembled in #37008]
37001    43.296711    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=5920, ID=133e) [Reassembled in #37008]
37002    43.296713    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=7400, ID=133e) [Reassembled in #37008]
37003    43.296716    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=8880, ID=133e) [Reassembled in #37008]
37004    43.296718    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=10360, ID=133e) [Reassembled in #37008]
37005    43.296720    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=11840, ID=133e) [Reassembled in #37008]
37006    43.296723    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=13320, ID=133e) [Reassembled in #37008]
37007    43.296726    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=14800, ID=133e) [Reassembled in #37008]
37008    43.296728    172.18.0.3    172.18.0.5    NFS    274    V3 READ Reply (Call In 36996) Len: 16384
Then, the next read would be issued by the receiver, with a similar response from the sender:
Code:
37009    43.313577    172.18.0.5    172.18.0.3    NFS    178    V3 READ Call (Reply In 37021), FH: 0xc071e444 Offset: 46628864 Len: 16384
37010    43.313640    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=0, ID=133f) [Reassembled in #37021]
37011    43.313643    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=1480, ID=133f) [Reassembled in #37021]
37012    43.313646    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=2960, ID=133f) [Reassembled in #37021]
37013    43.313648    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=4440, ID=133f) [Reassembled in #37021]
37014    43.313650    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=5920, ID=133f) [Reassembled in #37021]
37015    43.313653    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=7400, ID=133f) [Reassembled in #37021]
37016    43.313656    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=8880, ID=133f) [Reassembled in #37021]
37017    43.313658    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=10360, ID=133f) [Reassembled in #37021]
37018    43.313660    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=11840, ID=133f) [Reassembled in #37021]
37019    43.313663    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=13320, ID=133f) [Reassembled in #37021]
37020    43.313666    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=14800, ID=133f) [Reassembled in #37021]
37021    43.313668    172.18.0.3    172.18.0.5    NFS    274    V3 READ Reply (Call In 37009) Len: 16384
However, the receiver seemingly ignores the sent data and keeps re-issuing the call for the set maximum number of retries, before timing out and giving up:
Code:
37035    44.411279    172.18.0.5    172.18.0.3    NFS    178    [RPC retransmission of #37009]V3 READ Call (Reply In 37021), FH: 0xc071e444 Offset: 46628864 Len: 16384
37036    44.411365    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=0, ID=1341) [Reassembled in #37047]
37037    44.411368    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=1480, ID=1341) [Reassembled in #37047]
37038    44.411371    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=2960, ID=1341) [Reassembled in #37047]
37039    44.411373    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=4440, ID=1341) [Reassembled in #37047]
37040    44.411375    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=5920, ID=1341) [Reassembled in #37047]
37041    44.411378    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=7400, ID=1341) [Reassembled in #37047]
37042    44.411381    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=8880, ID=1341) [Reassembled in #37047]
37043    44.411383    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=10360, ID=1341) [Reassembled in #37047]
37044    44.411386    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=11840, ID=1341) [Reassembled in #37047]
37045    44.411389    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=13320, ID=1341) [Reassembled in #37047]
37046    44.411392    172.18.0.3    172.18.0.5    IPv4    1514    Fragmented IP protocol (proto=UDP 17, off=14800, ID=1341) [Reassembled in #37047]
37047    44.411394    172.18.0.3    172.18.0.5    NFS    274    [RPC duplicate of #37021]V3 READ Reply (Call In 37009) Len: 16384
The number of retries can be increased to any amount but it will never succeed, and this is with no other network traffic, always repeatable to a certain position in the file being read. Other NFS traffic (e.g. a directory listing) would succeed while this read operation was in timeout / retransmission, indicating that it was not a problem with general NFS connectivity.

It will get one or two reads past that sometimes but it seems more like there are just a few in-flight than any actual progression.

I am not entirely sure what causes this, whether IRIX bug or an artifact of the fast sender (GigE) to slow receiver (10M) and potentially overflowing switch buffers? However reducing rsize in the IRIX (client) mount options to reduce the number of outstanding fragments made things work. rsize=4096 was the closest doubling number up from rsize=1024 (first below MTU) that worked for me. I am curious if anyone has encountered similar issues?

I did not reduce wsize on the IRIX client because presumably the fast link / modern FreeBSD NFS server (which would be the recipient of any writes) has no such issues.

Notably I did not have these issues on other IRIX machines connected by faster links, but I don't know whether I was using the same IRIX release (may have been using 6.5.26).
 
Last edited:

Elf

Storybook
Feb 4, 2019
567
155
43
I suppose I spoke too soon; on a much bigger file I had to reduce all reads to below MTU with rsize=1024 😭
I sort of want to try a 100 mbit full duplex Phobos card now to see if it makes any difference. The Indigo 2 and up seem to do just fine.
 

Elf

Storybook
Feb 4, 2019
567
155
43
Well between switching over to a Phobos 100mbit card and upgrading to 6.5.22 the problem still happens. Not sure whether to leave this thread in hardware or move it to software 😄
 

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