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SubjectRe: The good, the bad & the ugly (or VM, block devices, and SCSI :-)


On Thu, 1 Nov 2001, Stephan von Krawczynski wrote:

> On Wed, 31 Oct 2001 18:29:25 +0100 (CET) Gérard Roudier <groudier@free.fr>
> wrote:
>
> > > A29160: symbios:
> > >
> > > cd read without nfs-load: cd read without nfs-load
> > > 2998,9 kB 3619,3 kB
> > > 3168,2 kB 3611,1 kB
> > > 2968,4 kB 3620,2 kB
> > >
> > > cd read with nfs load: cd read with nfs load
> > > 1926,2 kB 3408,1 kB
> > > 2123,4 kB 3395,2 kB
> > > 2539,4 kB 3605,1 kB
> > > 2631,9 kB 3605,8 kB
> > >
> > > [...]
> > > My personal opinion: Justin has work to do.
> >
> > Agreed here. Justin should write a clean SCSI access method for Linux for
> > free as he did for FreeBSD. :-)
>
> Just to make that clear: its not that I am in the position of _expecting_
> anything. I only want to give a clear hint what (according to my limited
> knowledge) the problem might be, and who could possibly solve it.

That was clear. As clear it is that my reply here was kind of joke. :)

> > Just considering the CD read thoughtput differences, we cannot get any
> > useful information that applies to software driver differences from your
> > report. Given the very low throughput it involves (about 3 MB/s) compared
> > to the capabilities of the controllers (160 MB/s), the results should be
> > explainable by something related to difference in configuration or to some
> > hardware or kernel weirdness.
>
> Well, what more can you expect from me, than the simple truth that the config
> is the _same_ for both tests and the only thing I am doing is exchange the
> scsi-controller (and therefore the used kernel-driver within the compiled
> bzImage).

I can beleive that.

> It is pretty clear that U160 cannot be reached by the CD-drive, because it is
> located on the scsi-2 connector (50 pin internal). It is a TEAC CD-532S which
> has (to my knowledge) not even wide-scsi but 8 bit data transfer). It is
> specified as being 30x, so should have a max throughput of 4500 kB/s (150 kB/s
> x 30). The values (at least symbios) are obviously not that far off, taking
> into account that 30x means "somewhere on the disk we reach 30x" and not
> "through the whole disk we have 30x".
> The only difference I can confirm is in TCQ-depth being configured to 8 on
> adaptec and 4 (!) on tekram. I reduced the tcq-depth on adaptec from 256 to 8,
> because
> a) 256 doesn't work out anyway. I got switched back to 128 during workload
> according to the driver
> b) even 128 makes "feelable" latency during heavy I/O and concurrent
> shell-typing stuff.
> c) choose therefore 8, because the _old_ aic7xxx driver used 8, too, and was in
> my opinion better in terms of latency _and_ throughput (but didn't compile any
> more in some 2.4.x kernel, that's why I _had_ to switch over)

The TCQ-depth shouldn't matter as long as only the CD drive is accessed
given that such devices are unlikely to support tagged commands.
Nevertheless, you should check your boot log messages and also compare the
thoughput negotiation between controller and devices.

> some additional infos:
> Motherboard Asus CUV4X-D, 2 x P-III 1 GHz, 1 GB RAM
>
> /proc/scsi/scsi:
>
> Attached devices:
> Host: scsi0 Channel: 00 Id: 08 Lun: 00
> Vendor: IBM Model: DDYS-T36950N Rev: S96H
> Type: Direct-Access ANSI SCSI revision: 03
> Host: scsi1 Channel: 00 Id: 02 Lun: 00
> Vendor: BNCHMARK Model: DLT1 Rev: 391B
> Type: Sequential-Access ANSI SCSI revision: 02
> Host: scsi1 Channel: 00 Id: 03 Lun: 00
> Vendor: TEAC Model: CD-ROM CD-532S Rev: 1.0A
> Type: CD-ROM ANSI SCSI revision: 02
> Host: scsi1 Channel: 00 Id: 05 Lun: 00
> Vendor: TEAC Model: CD-R58S Rev: 1.0P
> Type: CD-ROM ANSI SCSI revision: 02
> Host: scsi1 Channel: 00 Id: 06 Lun: 00
> Vendor: HP Model: C1537A Rev: L005
> Type: Sequential-Access ANSI SCSI revision: 02
>
> /proc/interrupts (tekram):
> CPU0 CPU1
> 0: 77797 76618 IO-APIC-edge timer
> 1: 3127 2991 IO-APIC-edge keyboard
> 2: 0 0 XT-PIC cascade
> 5: 74 83 IO-APIC-level HiSax
> 8: 1 1 IO-APIC-edge rtc
> 9: 4651 4171 IO-APIC-level EMU10K1, eth0
> 10: 16563 16459 IO-APIC-level sym53c8xx, sym53c8xx, eth2
> 11: 62677 62214 IO-APIC-level eth1, nvidia
> 12: 8842 8772 IO-APIC-edge PS/2 Mouse
> 14: 143 29 IO-APIC-edge ide0
> NMI: 0 0
> LOC: 154305 154182
> ERR: 0
> MIS: 0
>
> /proc/interrupts (adaptec):
> CPU0 CPU1
> 0: 5967 5266 IO-APIC-edge timer
> 1: 209 192 IO-APIC-edge keyboard
> 2: 0 0 XT-PIC cascade
> 5: 9 6 IO-APIC-level HiSax
> 8: 1 1 IO-APIC-edge rtc
> 9: 183 175 IO-APIC-level EMU10K1, eth0
> 10: 2309 2172 IO-APIC-level aic7xxx, eth2
> 11: 3532 3468 IO-APIC-level eth1, nvidia
> 12: 920 1103 IO-APIC-edge PS/2 Mouse
> 14: 124 48 IO-APIC-edge ide0
> NMI: 0 0
> LOC: 11124 10979
> ERR: 0
> MIS: 0

Indeed, the configs look very similar.

> And yes: eth2 is exactly the device where the nfs-load is coming from. This is
> unintentional, it just worked out this way, but equal for both contestants.
> And no: unfortunately I cannot manage to come to a config where the scsi-IRQ is
> singular, I tried hard today, but the network is in fact a 4-port tulip card
> which makes a pci-bridge and the irqs behind the bridge tend to do whatever
> they like. In fact I moved the irq for the scsi-controllers via bios, but guess
> what: eth2 followed wherever I went.

PCI defines 4 interrupt lines per slot and also defines some rules for
interrupt lines wiring behind bridges. OTOH, the routing glue to the
interrupt controller may well not allow all possible combinations. What
happens could just be that the routing glue just hardwires the both
interrupt lines here, and only moving a PCI board to another slot can
allow to use different IRQs for the 2 devices.

> Keep in mind, even with no network traffic adaptec performs bad.
> Ah and another thing, I tried _several_ adaptec controllers (even a 29160N),
> all the same results.
>
> > I cannot believe a single second that the
> > difference is due to the software drivers.
>
> I can. I did a whole lot of such tests during my former job for a company
> producing scsi-controllers.

Interesting, if you can elaborate...

> > Thanks, anyway, for your report.
>
> Well, as already said, take it as a hint that your part of the story performs
> pretty well.
> ;-)

The sym53c8xx driver beeing faster than the aic7xxx with CD devices using
Ultra160 controllers is an amuzing result. :)
I still cannot beleive that it is due to a aic7xxx driver fault. If I had
such a controller, I would for sure check that, but I haven't any.

Regards,
Gérard.

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