Date: Sat, 8 Apr 1995 14:50:19 +0800 (CST) From: Brian Tao <taob@gate.sinica.edu.tw> To: FREEBSD-CURRENT-L <freebsd-current@FreeBSD.org> Subject: Re: Disk performance Message-ID: <Pine.BSI.3.91.950408140448.787A-100000@aries.ibms.sinica.edu.tw> In-Reply-To: <199504071634.JAA07710@gndrsh.aac.dev.com>
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On Fri, 7 Apr 1995, Rodney W. Grimes wrote:
>
> > 'top' shows this (sometime during the latter half of the run):
> >
> > PID USERNAME PRI NICE SIZE RES STATE TIME WCPU CPU COMMAND
> > 20444 root 48 0 244K 424K run 0:41 51.76% 50.35% iozone
>
> I get the following stats using 3 different utilities (I was glad to
> see that thy agreed within reason!): [We are not comparing apples to
> apples here, I am running on a P54C-90, your tests where on a DX4/100]
>
> systat -vm processor mode line:
> 19.3%Sys 2.0%Intr 0.5%User 0.0%Nice 78.3%Idl
I asked because the P90 (the one with those twin Maverick drives)
peaks at less than 10% CPU, but of course it can barely manage
1.3MB/sec with iozone so the CPU is idle 90% of the time. Thus my
initial reaction to the 50% figure above was "too high", and so:
> > Is this a reasonable figure?
>
> You forgot that the CPU is not 100% busy.
My feeling is that it should have been lower and not anywhere
close to 100% usage. Sending out 366 I/O requests to a SCSI device
and waiting for them to return did not seem to warrant a 50% busy
state with a 100-MHz processor on a 33-MHz bus. I gather this is
where IDE drives fare much worse?
> What that 2.7mS number
> relates to closest is the fact that 8192 bytes fly under the disk head
> in ~2.7mS. Your Quantum 1080 is a 5400 RPM (90 RPS) drive, meaning
> it takes 11.11mS for one revolution, turning a few more numbers through
> xcalc 2.7mS/11.11mS * (16 sectors per 8192 bytes)=65 sectors/revolution.
You mean 11.11/2.7, but I get your point. Quantum's data sheet
for the Empire 1080 shows 64 to 107 sectors per track. I tested it
on my sd0g partition which is located between cylinders 467 to 862
(out of 1017). The iozone file is probably located along the inner
half of that cylinder group, given that the filesystem is over half
ful now. So given the overheard in iozone and other little errors, 65
sectors/track is pretty good guess.
BTW, is the best place for a swap partition along the outer edge
of the disk where there are more sectors/track, or are there other
factors (e.g., disk head seeking between swap and ufs partitions)?
Does it really make much difference with only one spindle to swap on?
> > % time dd if=/dev/zero of=/dev/null bs=102400 count=10240
>
> It is hard to be sure exactly what is being measure here, It is
> a combination of bzero speed, RAM -> CPU and CPU <-> cache bandwidths.
[...]
> I tried to correlate the number with a memory benchmark program on
> my system and it comes up to be faster than the CPU -> main memory
> write bandwidth but about 1/2 the speed of main memory read bandwidth.
The P90 gets roughly the same benchmark (if you could call it
that) as both the DX4/100 and DX2/66, about 33MB/sec. The Sparc1
upstairs gets 13.3MB/sec but the SGI Crimson next door gets something
like 128MB/sec. Probably not much more useful on its own than any
other benchmark.
--
Brian ("Though this be madness, yet there is method in't") Tao
taob@gate.sinica.edu.tw <-- work ........ play --> taob@io.org
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