strange i/o and tty lockups/delays on 6.1, strange sync() issue

[Rainer Hurling]

Hi Marek,

a thread on stable@ is dealing with this kind of hangings:

http://www.nabble.com/forum/ViewPost.jtp?post=13296788

Perhaps there is some relationship between them?

Regards,
Rainer


Marek Blaszkowski schrieb:
> Hi,
> my config:
> thunder k8sr, dual opteron 244, 8GB RAM, FreeBSD 6.1, sata disk
> 
> 
> for time to time (every 10 or 20 secs) any process which try write or read any, even small file,
> is locked for a couple seconds (about 7 or 9 secs), very iritating when I try save
> small files edited in vim (size about 2-3 kbytes), it's looks like this:
> #vim /path/to/file
> ...editing..
> :w
> and now (afetr w command) vim freeze for 7-10 secs until it displays "file written".
> 
> Delays accours on tty, too. In vim I can't move around edited file (up/down in rows),
> vim just got hang, strange is that I can switch (durning vim lockup) beetwen virtual screen
> consoles.
> 
> System is not swapping (4GB ram free), iostat says:
> 
> #iostat 1
>       tty             ad4              ad6             cpu
>  tin tout  KB/t tps  MB/s   KB/t tps  MB/s  us ni sy in id
>    1  353 17.94  45  0.78   0.64   0  0.00  11  1  6  1 82
>    0  360 16.00  72  1.12   0.00   0  0.00  17  0  2  1 81
>    0  120 16.00  77  1.20   0.00   0  0.00   6  0  3  1 90
>    0  120 14.66  73  1.04   0.00   0  0.00  41  0 11  1 47
>    0  120 16.00  78  1.22   0.00   0  0.00  27  0  1  0 72
>    0  120 16.22  74  1.17   0.00   0  0.00   0  0  0  0 100
>    0  122 17.22  79  1.33   0.00   0  0.00   8  1  5  0 85
>    0  120 16.46  79  1.27   0.00   0  0.00  14  0  3  2 81
>    0  120 13.85  48  0.65   0.00   0  0.00   7  0  4  0 88
>    0  120 15.13  79  1.17   0.00   0  0.00  12  0  4  1 83
>    0  120 11.11  83  0.90   0.00   0  0.00   8  0  3  1 89
> 
> as You see, there is no heavy i/o load.
> 
> Strange things is I have two identical setup of the same system configuration with the same
> apps running (web server mirror) but other motherboard (K8W), on the second system there no such delay/lockup
> issue.
> It's looks like some other process calls sync() on every 7 or 10 seconds and it couse such i/o delay.
> Other question is why sync takes so much time, when i/o disk performance its not bad (tested with dd is about 50MB/sec)
> and iostat (durning sync calls) doesn't show any high disk transfers.
> Example:
> #time sync
> real    2m0.853s
> user    0m0.000s
> sys     0m0.145s
> 
> 2 mins was the longest time amount I saw durning tests, in most cases sync takies about 10 secs, when sync was called on the
> other tty iostat doesn't print any high transfer, never it exceed 1MB/s.
> Qestion is: if disks transfers (using cp or dd) are high, why sync waits so long ?
> 
> I played with vfs.write_behind=0 but it doesn't change anything.
> 
> PS.
> I checkced motherboards manuals: K8W and K8SR have the same sata chip (Silicon Image SIL3114), so I think
> above problems are not ata driver issues.
> 
> regards,