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2.6.11-rc3: 80-95% systime when serving files via NFS

To: linux-xfs@xxxxxxxxxxx
Subject: 2.6.11-rc3: 80-95% systime when serving files via NFS
From: Anders Saaby <as@xxxxxxxxxxxx>
Date: Mon, 7 Feb 2005 23:45:30 +0100
Organization: Cohaesio A/S
Sender: linux-xfs-bounce@xxxxxxxxxxx
User-agent: KMail/1.7.2
Hi List,

At the moment we are testing an NFS server based on a Xeon Nocona (em64t) and 
2.6.11-rc3 compiled for X86_64/em64t as the machine has 8GB memory.

Filesystem is based on XFS with external journal.

This is a top snip when the server is under heavy read load:

<TOP>
top - 23:02:25 up  5:14,  6 users,  load average: 8.54, 9.51, 8.99
Tasks: 122 total,   6 running, 116 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.3% us, 92.4% sy,  0.0% ni,  0.0% id,  5.0% wa,  0.0% hi,  2.3% si
Mem:   8226600k total,  6946504k used,  1280096k free,     4212k buffers
Swap:        0k total,        0k used,        0k free,  6203480k cached
</TOP>

As you can see, the systime is ~90%.

I saw an earlier mail from Nathan regarding xfs_iget_core optimizations in 
december, but as the following kernel profile shows, this procedure is 
responsible for most of the load:

This is a kernel profile at the same time:

<PROFILE SNIP>
 99621 total                                      0,0387
 56322 xfs_iget_core                             45,1298
 33711 mwait_idle                               234,1042
  4500 xfs_iextract                              10,8173
  1077 __do_softirq                               5,6094
   284 tg3_start_xmit                             0,1830
   272 tg3_rx                                     0,2464
   201 *unknown*
   199 tg3_interrupt                              0,5923
</PROFILE SNIP>

- Is this expected behavior? - or is something wrong (I would like to think 
so :-))

- If you need any additional info I will be happy to provide it!

NOTE: This behavior does not show unless most of the memory is used for cache 
(Right after reboot, systime is ~5%).

NOTE2: When only serving files which is already in cache systime also drops to 
~5-10%

-- 
Med venlig hilsen - Best regards - Meilleures salutations

Anders Saaby
Systems Engineer
------------------------------------------------
Cohaesio A/S - Maglebjergvej 5D - DK-2800 Lyngby
Phone: +45 45 880 888 - Fax: +45 45 880 777
Mail: as@xxxxxxxxxxxx - http://www.cohaesio.com
------------------------------------------------


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