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Date:      Fri, 22 Apr 2005 09:56:50 -0600
From:      Scott Long <scottl@samsco.org>
To:        Daniel Eriksson <daniel_k_eriksson@telia.com>
Cc:        'FreeBSD Current' <freebsd-current@freebsd.org>
Subject:   Re: Serious I/O problems (bad performance and live-lock)
Message-ID:  <42691EC2.7080106@samsco.org>
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Daniel Eriksson wrote:
> With recent CURRENT (at least for the last 2 days, but probably longer), two
> of my systems can be brought to their knees (live-lock) with a simple "dd
> if=/dev/zero of=test bs=128k" command. I have not tested any other systems.
> 
> I keep both servers synced running 6-CURRENT:
> 
> Server #1: dual AthlonMP 2600+, Compaq SmartArray 5302/64 hardware raid card
> (ciss). The card hosts two arrays, one RAID-5 built from 4 discs that holds
> the system and one RAID-0 built from 14 discs. All the discs are 36GB 10krpm
> and I have one array on each channel on the card.
> 
> Server #2: AthlonXP 2500+ with an old Maxtor 27GB UDMA66 disc for the
> system.
> 
> 
> What made me take notice was that server #2 ran through a "make
> installkernel; make installworld" faster than server #1 during a recent
> upgrade. This makes no sense given the superior I/O performance of the
> hardware scsi raid array on server #1, and I know that in the past server #1
> has finished the process ahead of server #2.
> 
> After the upgrade was done I ran some simple tests with 'dd', and it only
> took ~1 minute for the system to live-lock. Breaking into DDB and killing
> the 'dd' process brought the machine back to life. I assumed the problem was
> ciss-related, CAM-related or SMP-related, but I just tried doing the same
> thing on the UP machine (server #2), and it too live-locked within a minute.
> 
> Both systems use pretty much the same config, with the only major difference
> being SMP or not:
> * SCHED_4BSD, PREEMPTION, ADAPTIVE_GIANT, DEVICE_POLLING, HZ=2000
> * debug.mpsafenet="1", debug.mpsafevfs="1"

What happens if you turn off mpsafevfs?

Scott



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