Re: Poor performance during disk writes

["Gérard Roudier" <groudier@free.fr>]

On Tue, 18 Dec 2001, Andre Hedrick wrote:

> On Tue, 18 Dec 2001, Gérard Roudier wrote:
>
> >
> >
> > On Tue, 18 Dec 2001, Andre Hedrick wrote:
> >
> > > File './Bonnie.2276', size: 1073741824, volumes: 1
> > > Writing with putc()...  done:  72692 kB/s  83.7 %CPU
> > > Rewriting...            done:  25355 kB/s  12.0 %CPU
> > > Writing intelligently...done: 103022 kB/s  40.5 %CPU
> > > Reading with getc()...  done:  37188 kB/s  67.5 %CPU
> > > Reading intelligently...done:  40809 kB/s  11.4 %CPU
> > > Seeker 2...Seeker 1...Seeker 3...start 'em...done...done...done...
> > >               ---Sequential Output (nosync)--- ---Sequential Input-- --Rnd Seek-
> > >               -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --04k (03)-
> > > Machine    MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU   /sec %CPU
> > >        1*1024 72692 83.7 103022 40.5 25355 12.0 37188 67.5 40809 11.4  382.1  2.4
> > >
> > > Maybe this is the kind of performance you want out your ATA subsystem.
> > > Maybe if I could get a patch in to the kernels we could all have stable
> > > and fast IO.
> >
> > I rather see lots of wasting rather than performance, here. Bonnie says
> > that your subsystem can sustain 103 MB/s write but only 41 MB/s read. This
> > looks about 60% throughput wasted for read.
> >
> > Note that if you intend to use it only for write-only applications,
> > performance are not that bad, even if just dropping the data on the floor
> > would give you infinite throughput without any difference in
> > functionnality. :-)
>
> Well sense somebody paid/paying me make write performance go through the
> roof -- that is what I did.  Now if you look closely you could see that in
> writing we are doing a boat load more work than reading.  If somebody want
> me to throttle the reads more then they know how to get it done.

I am not the one that will pay you for that, as you can guess. :-)

I just was curious about the technical reasons, if any, of so large a
difference. Just, the CPU and the memory subsystem are certainly not the
issue. But I donnot want to prevent you from earning from such kind of
improvement. Hence, let me go back to free scsi.

  Gérard.

> Regards,
>
> Andre Hedrick
> Linux Disk Certification Project                Linux ATA Development