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SubjectRe: SMP 2.1.131: SCSI performance extremely poor vs. IDE


On Sun, 13 Dec 1998, Doug Ledford wrote:

> Chris wrote:
> >
> > >>>>> "Lawrence" == Lawrence Walton <lawrence@otak-k.com> writes:
> >
> > Lawrence> I wonder about the bonnie benchmarking, but here is a
> > Lawrence> SCSI benchmark with bonnie and a Symbios 875 and a 18
> > Lawrence> barracuda, P233 and 128 megs of ram. Linux version
> >
> > Lawrence> How does this stack up? is it a SMP only thing?
> >
> > Just as a side note, bonnie benchmarks of a size less than several
> > times RAM, are just a test of memory bandwidth, since a large portion
> > gets cached. Try comparing those numbers to a 800 - 1000 meg test...
> >
> > Heck, I've seen read rates of over 50meg/sec off of some small
> > tests ;) If you want to see some benchmarks to compare against look
> > at the bonnie results at
> >
> > http://www.tec.ualberta.ca/Benchmarks/benchmarks.html
>
> Those particular numbers all look to be from fairly dated hardware.
> With somewhat modern hardware (5 Seagate Cheetah Ultra2 drives on two
> Ultra2 channels on one 3950U2b Adaptec controller all in a RAID0 array
> in a PII 266 box with 128MB RAM) I'm seeing numbers like these:
>
> 2.0.36UP:
> -------Sequential Output-------- ---Sequential Input-- --Random--
> -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
> MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU /sec %CPU
> 512 12020 98.2 65325 89.0 14788 50.0 14585 94.2 65283 86.7 255.1 5.5
> 512 12018 98.2 64312 87.8 14975 49.8 14707 95.3 65065 85.4 251.4 5.2
> 512 12041 98.2 66525 91.7 15027 50.2 14801 95.6 63949 86.2 258.8 5.6

Unfortunately I am not able to run such benchmarks since my penis is not
as long as 5 Cheetah2, but just as one of such beast, but I can comment.

5 Cheetah2 -> something like 18x5 = 90 MB/sec sustaint in the 1rst 512 MB
of each. If I assume your RAID0 has been optimized and that you are using
a not patched kernel, block read number shows the following:

IO/sec -> 65000*5/76=4300 IOs/sec of 15K chunk in average.

I am not way impressed by these numbers when using 2 LVD SCSI channels.
You probably stressed the memory, but probably not the SCSI BUS and your 2
LVD SCSI channels with your benchmark.

I am a lot more interested in results using 3 or 4 Cheetah2 on 1 SCSI
channel for sustaint data rate and in the actual latency of SCSI commands
for short IOs using these 2, 3 or 4 Cheatah2 at a time on a single SCSI
channel.

> The numbers I have for 2.1.131 so far are all SMP numbers and so can't
> be compared against the 2.0.36 numbers. I plan on getting some UP
> numbers for 2.1.131 as well before too long.

If you intend to measure some kernel difference in handling IOs, then
such results may make sense, but they are not relevant with regards to
the ability of your SCSI controllers to perform IOs, in my opinion.
Bonnie is a great liar, and we must be very careful when posting
Bonnie benchmarks. Indeed, your post has been sent to the kernel list,
so you are not off-topic. This would be different if you posted it to
the scsi list.

Regards,
Gerard.





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