Folks,
Ok, I was able to crack the issue but in some odd way. I found that
pdflush was not able to flush the buffers in time because of which the
next write requests were stalled at the client side. I did following
changes to improve the performance.
1. Changed the number of pdflush threads from default 2 to 4
2. Changed the CACHESIZE from 1024 to 8192 in fs/nfsd/nfscache.c
3. Changed SVC block size from 32k to 64k in include/linux/nfsd/const.h
After these changes, as expected I see much better performance but then
there is overshoot of at the start with less write size and later it
decreases. I captured the iozonelinux figures and they are as below
Excel output is below:
"Writer report"
"4" "8" "16" "32" "64"
"65536" 1006667 1414856 1437128 1606784 1580778
"131072" 801006 1427892 1232945 1191835 1232504
"262144" 8555 16856 10093 16721 12607
"524288" 8136 13017 8419 11485 16160
"1048576" 6546 9635 10923 10611 10995
"Re-writer report"
"4" "8" "16" "32" "64"
"65536" 1323668 1512831 1645809 1757521 1792708
"131072" 1119661 1299879 1367497 1423008 1427222
"262144" 3290 4173 3494 4158 4969
"524288" 3268 3398 3200 2899 3570
"1048576" 3126 3183 3646 3231 3890
"Reader report"
"4" "8" "16" "32" "64"
"65536" 10790 11167 11123 10842 9409
"131072" 9270 10640 9084 9480 10958
"262144" 10136 11011 10881 8924 8911
"524288" 10947 9303 8567 9290 10853
"1048576" 10290 9499 10956 11156 11063
"Re-Reader report"
"4" "8" "16" "32" "64"
"65536" 1770290 591736 686075 240800 236228
"131072" 753296 1219558 858200 1142548 1080169
"262144" 611654 308045 521012 403101 854802
"524288" 10834 9075 10613 9219 2725002
"1048576" 1410151 2341711 2635044 2869093 3004842
"Writer CPU utilization report (Zero values should be ignored)"
"4" "8" "16" "32" "64"
"65536" 0.79 0.44 0.71 0.56 0.57
"131072" 0.75 0.78 0.57 0.67 0.72
"262144" 0.61 0.55 0.56 0.61 0.56
"524288" 0.68 0.58 0.59 0.26 0.59
"1048576" 0.61 0.68 0.67 0.68 0.68
"Re-writer CPU utilization report (Zero values should be ignored)"
"4" "8" "16" "32" "64"
"65536" 0.70 0.66 0.59 0.52 0.70
"131072" 0.29 0.24 0.20 0.21 0.20
"262144" 0.25 0.22 0.19 0.20 0.20
"524288" 0.26 0.25 0.22 0.20 0.21
"1048576" 0.27 0.23 0.21 0.20 0.20
"Reader CPU utilization report (Zero values should be ignored)"
"4" "8" "16" "32" "64"
"65536" 1.17 0.92 1.14 0.93 0.75
"131072" 1.00 1.17 0.80 0.79 1.07
"262144" 1.17 1.11 0.88 0.73 0.77
"524288" 1.19 0.90 0.77 0.78 0.84
"1048576" 1.13 0.91 0.99 0.94 0.87
"Re-Reader CPU utilization report (Zero values should be ignored)"
"4" "8" "16" "32" "64"
"65536" 97.38 27.73 28.08 10.25 8.97
"131072" 41.15 57.14 33.57 43.21 44.13
"262144" 33.04 14.79 22.96 15.20 32.82
"524288" 1.15 0.81 0.93 0.75 93.97
"1048576" 71.14 99.75 99.18 99.22 99.61
I am surprised to see that write performance is better than read and
more interestingly re-write performance is degraded compared to write
performance.
Any cluses on this anomaly?
Thanks in advance
Sagar
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Sagar Borikar
Sent: Tuesday, February 12, 2008 2:04 PM
To: [email protected]
Subject: nfs performance dropped when using 128 MB RAM
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