Re: bonnie++ uninterruptible under heavy I/O load

From: Denis Vlasenko (vda_at_port.imtp.ilyichevsk.odessa.ua)
Date: 03/11/05

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    To: Simone Piunno <simone.piunno@wseurope.com>, linux-kernel@vger.kernel.org, Fabio Coatti <fabio.coatti@wseurope.com>
Date:	Fri, 11 Mar 2005 13:35:56 +0200

    On Friday 11 March 2005 13:08, Simone Piunno wrote:
    >
    > Hello,
    >
    > I'm testing a pair of new servers we just bought.
    > They are HP DL585 dual Opteron 844 with 8G RAM, RAID1 over 2x72G SCSI disks
    > (HP CISS driver) and running 2.6.11. In /proc/driver/cciss/cciss0 we have:
    >
    > cciss0: HP Smart Array 5i Controller
    > Board ID: 0x40800e11
    > Firmware Version: 2.56
    > IRQ: 18
    > Logical drives: 1
    > Current Q depth: 0
    > Current # commands on controller: 0
    > Max Q depth since init: 6
    > Max # commands on controller since init: 190
    > Max SG entries since init: 31
    > cciss/c0d0: 72.83GB RAID 1(1+0)
    >
    > As a test, I'm running bonnie++ while two md5sum are checksumming /dev/zero.
    > I see 98% CPU is correctly allocated on the two md5sum processes, but when
    > bonnie is in the "Writing intelligently phase" the system appears noticeably
    > unresponsive (high latency) and bonnie and pdflush are uninterruptible almost
    > all the time (D in top output). If I try to kill -9 bonnie++, it goes on
    > consuming I/O bandwith for several tens of seconds, before finally dieing.
    >
    > Unresponsiveness is not 2.6.11 specific (we've seen the same thing on 2.6.10
    > and 2.6.8), not I/O scheduler specific ("as" and "deadline" behave the same)
    > and not CPU/SMP specific (reproduced on single P4 HT and single P3), but only
    > on these two DL585 servers we've seen bonnie++ resisting kill -9 for tens of
    > seconds.
    >
    > Of course on request I can provide any other useful info.
    > Any help is appreciated.

    I think Alt-SysRq-T will be interesting to see 

    --
vda
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