Hello Folks,
I am not sure if this is the right place for this question. If not, I am
sorry and request you to direct me to right mailing list.
Currently I am working on a product which is derived from its ancestor
with more or less similar feature set and few additions. Other than
memory size, there are not hardware changes. The newer one is having 128
MB RAM while the ancestor was having 512 MB of RAM. The functionality
carried forward is also similar except for nfs. Both have gigabit
Ethernet interfaces
I am finding that nfs write performance has drastically
reduced say 1 MB/s or even it stalls for large file transfers to the
box. On the contrary it works fine with 512 MB of RAM. The CPU
utilization by nfsd as well as rpc.statd / rpc.mountd is also non
existent. Rather nfsd most of the time is sleeping for the data. While
trying to analyse through ethereal, I observe that the write requests by
clients to the the server are periodic say around 1.5-2 minutes
interval. Till then the tcpdump captures that the handshake is going on
only for ack messages for wait requests. After then suddenly the burst
write transfer starts and within 4-5 seconds when the buffers are full
and no free memory is available, again it repeats the same cycle. When
poking in the meminfo stats, I found that there are no dirty pages and
write back buffers available before write bursts. As soon as the buffers
are available, nfs sends requests for further data and meminfo stats are
as it is. The free memory which is LowFree memory used by kernel data
structures in our case as High free memory is zero, is very less when
the buffers are not cleaned up. Once the burst data transfer finishes,
cached memory equal to that of previous buffered gets cleared as
expected. But Inactive memory is still high. I am attaching the tcpdump
logs with this mail. I am using rsize / wsize as 64k. Tried various
combinations of these sizes while mounting the nfs clients but it didn't
help.
I tried to check whether this problem is system wide but unfortunately
CIFS and FTP writes are pretty fast. so only nfs performance is affected
due to RAM size reduction. We have enabled socket buffer recycling in
Ethernet driver which block 600k of data for recycling. Even just to get
confirmation, I disabled the skb recycling, even then the result was
same. I am not seeing this kind of behavior in other workstations with
128 MB of RAM and mips architecture.
Can anyone let me know, why the write requests are buffered and
periodically they get cleared?
Also does nfs stack, requires special buffer availability for succeeding
write requests?
Thanks and Regards,
Sagar Borikar
PMC sierra
tcpdump.log
Description: tcpdump.log
