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Date:      Wed, 22 Nov 2006 19:41:46 +0000
From:      Dieter <freebsd@sopwith.solgatos.com>
To:        freebsd-questions@freebsd.org
Subject:   Re: processes not getting fair share of available disk I/O (was: Re: TCP parameters and interpreting tcpdump output ) 
Message-ID:  <200611230341.DAA04594@sopwith.solgatos.com>
In-Reply-To: Your message of "Wed, 22 Nov 2006 21:37:33 EST." <20061123023733.GA46545@xor.obsecurity.org> 

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> > > > > > time ls on a small directory on disk2
> > > > > >=3D3D20
> > > > > > real    4m51.911s
> > > > > > user    0m0.000s
> > > > > > sys     0m0.002s
> > > > > >=3D3D20
> > > > > > I expect access to a busy disk to take longer, but 5 minutes is
> > > > > > a bit much.  And that's the root directory of the filesystem,
> > > > > > it didn't have to follow a long chain of directories to get there.
> > > > > >=3D3D20
> > > > > > Sometimes I see long delays when accessing disk3, but it is
> > > > > > behaving at the moment.
> > > > >=3D20
> > > > > ls still has to acquire a number of locks in order to be sure that =
> the
> > > > > contents of the directory aren't changing.  If there are lots of ot=
> her
> > > > > processes all competing for these locks, it will be slow.  It looks
> > > > > like that's the case on your system, although details of your workl=
> oad
> > > > > have been trimmed from your email.
> > > >=3D20
> > > > In telnet window 1:
> > > >=3D20
> > > > cd /disk1/
> > > > cp -ip very_big_file /disk2/bar/	(the workload)
> > > >=3D20
> > > > In telnet window 2:
> > > >=3D20
> > > > time ls /disk3/foo1/  (make sure time and ls are cached in memory)
> > > > time ls /disk3/foo2/  (see timing numbers above)
> > > > time ls /disk2/       (see timing numbers above)
> > > >=3D20
> > > > The /disk2/ directory is small, only contains 3 directories and .snap
> > > >=3D20
> > > > Would the cp into /disk2/bar/ lock the /disk2/ directory?
> > >=20
> > > It shouldn't do.
> > >=20
> > > What scheduler are you using?
> >=20
> > kern.sched.name: 4BSD
> > kern.sched.quantum: 100000
> > kern.sched.preemption: 1
> 
> OK, that's correct.  Can you also provide details of your disk
> hardware (e.g. dmesg) and kernel configuration?

FreeBSD 6.0

Kernel is stock except for addition of:

	device                atapicam        # needed to burn dvd

/boot/loader.conf:

	console="comconsole"
	hw.ata.wc=0
	hw.ata.atapi_dma="1"
	kern.ipc.nmbclusters="256000"

Mainboard: Tyan Tomcat k8e 2865

CPU: AMD64 3000+

Chipset: Nvidia nforce4 ultra

Memory: 2 GB DDR400 ECC

Disks:  4x Seagate 7200 rpm SATA
	1x Seagate 7200 rpm PATA
	1x LG CD/DVD

atapci0: <nVidia nForce4 UDMA133 controller> port 0x1f0-0x1f7,0x3f6,0x170-0x177,0x376,0xe000-0xe00f at device 6.0 on pci0
ata0: <ATA channel 0> on atapci0
ata1: <ATA channel 1> on atapci0
atapci1: <nVidia nForce4 SATA150 controller> port 0x9f0-0x9f7,0xbf0-0xbf3,0x970-0x977,0xb70-0xb73,0xcc00-0xcc0f mem 0xfebfb000-0xfebfbfff irq 10 at device 7.0 on pci0
ata2: <ATA channel 0> on atapci1
ata3: <ATA channel 1> on atapci1
atapci2: <nVidia nForce4 SATA150 controller> port 0x9e0-0x9e7,0xbe0-0xbe3,0x960-0x967,0xb60-0xb63,0xb800-0xb80f mem 0xfebfa000-0xfebfafff irq 11 at device 8.0 on pci0
ata4: <ATA channel 0> on atapci2
ata5: <ATA channel 1> on atapci2
acd0: DVDR <HL-DT-ST DVDRAM GSA-4160B/A301> at ata0-master UDMA66
ad2: 305245MB <Seagate ST3320620A 3.AAC> at ata1-master UDMA100
ad4: 238475MB <Seagate ST3250823AS 3.03> at ata2-master SATA150
ad6: 238475MB <Seagate ST3250823AS 3.03> at ata3-master SATA150
ad8: 238475MB <Seagate ST3250823AS 3.03> at ata4-master SATA150
ad10: 305245MB <Seagate ST3320620AS 3.AAC> at ata5-master SATA150
cd0 at ata0 bus 0 target 0 lun 0



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