Subject: Re: [Fwd: [linux-audio-dev] info point on linux hdr]
From: Benno Senoner (sbenno_AT_gardena.net)
Date: Mon Apr 17 2000 - 21:06:17 EEST
On Mon, 17 Apr 2000, Paul Barton-Davis wrote:
> Acknowledging your much greater wisdom in this are than me, I don't
> understand the above given that, in my experience:
>
> 1) pre-allocation takes a *long* time. Allocating 24 203MB files on a
> clean ext2 partition of 18GB takes many, many minutes, for example.
> Presumably, the same overhead is being incurred when block
> allocation happens "on the fly". If so, then even if pre-allocation
> doesn't solve the buffer cache write batching problem, it certainly
> gets rid of what appears to be an onerous task.
>
> 2) Why am I not having any of these problems ? Unlike Benno's code, I
> have a working application that runs just fine. I get smooth
> throughput from the disk subsystem too.
What do you mean exactly with "unlike Benno's code" ?
My code just tries to simulate the operation of a busy harddisk recorder
using the sorting algorithm to support variable speed.
I read in 256kb chunks too therefore I don't see a big difference between
my code and yours form a disk IO subsystem POV.
Anyway, I am running on EIDE disks, and you may experiency
less bursty IO since you are running on a SCSI disk.
Therefore it would be useful if you could run my benchmark on your
disk to see if your (or my approach) gets better performance out of the disk,
and with how much buffer utilization.
>
> Kernel 2.3.52 Kernel 2.3.52
> Dual PII-450 Dual PII-450
> on-board Adaptec 7890 on-board Adaptec 7890
> Seagate 4.5GB Cheetah U2W 10K rpm IBM 9GB UltraStar U2W 10K rpm
> Quantum 4.5GB Viking U2W 7.5K rpm 3 x IBM 18GB UltraStar
>
> In both cases, without O_SYNC, or anything else but preallocation
> and careful design, I seem to be able to get smooth disk throughput
> at significantly above the rate I need (9MB/sec; I get up to
> 17MB/sec from the UltraStar)
17MB/sec using hdparm or linear large reads/writes ( large cat / cp etc) or
17MB/sec within your harddisk recording app where
num_tracks * datarate_of_each_track = 17MB/sec
(it if's the latter then I doubt it because seek kills some of the throughput,
that's almost unavoidable, at least on my EIDE UDMA disks)
>
> In every case, I am doing disk I/O from a dedicated thread to a
> single disk.
>
> I'm confused. Is it just that I'm running on a genuine SMP system ?
SMP helps a bit, it increases throughput, although not significanltly
(i tried this on my dual Celeron both in SMP and UP mode)
Benno.
>
> --p
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