Re: [PATCH 6/9] clockpro-clockpro.patch

Peter Zijlstra
2006-01-25T08:00:59Z

Iwamoto-San,

On Tue, 2006-01-24 at 16:25 +0900, IWAMOTO Toshihiro wrote:
> (Removed linux-kernel@ from Cc:)
>
> At Tue, 24 Jan 2006 15:30:10 +0900,
> IWAMOTO Toshihiro wrote:
> > I thought this situation means that page access frequencies cannot be
> > correctly compared and leads to suboptimal performance, but I couldn't
> > prove that. However, I've managed to create an example workload where
> > clockpro performs worse. I'm not sure if the example is related to
> > this hand problem. I'll describe it in the next mail.
>
> Environment: Dell 1850 4GB EM64T CPUx2 HT disabled, x86_64 kernel
> Kernel 1: linux-2.6.15-rc5
> Kernel 2: linux-2.6.15-rc5 + clockpro patch posted in 2005/12/31
> Kernel 3: linux-2.6.15-rc5 + clockpro patch posted in 2005/12/31 +
> modification to disable page cache usage from ZONE_DMA
> (to rule out possible zone balancing related problem)
> Kernel 1 and 2 were booted with "mem=1008m", Kernel 3 was booted with
> "mem=1024m".
>
> The test program: 2read.c (attached below)
> 2read.c repeatedly reads from two files zero and zero2.
> Command line arguments specify the ranges to be read. (See the
> code for detail)
> It prints the number of read operations/2 every 5 seconds and
> terminates in 5 minutes.
>
> $ cc -O 2read.c
> $ ls -l zero*
> -rw-r--r-- 1 toshii users 1073741824 2006-01-13 17:27 zero
> -rw-r--r-- 1 toshii users 1572864000 2006-01-20 18:20 zero2
>
> (with Kernel 1)
> $ for n in 100 200 300 400 500; do
> > ./a.out -n $n $((1100-$n)) > /tmp/2d.$n ; done
> (with Kernel 2)
> $ for n in 100 200 300 400 500; do
> > ./a.out -n $n $((1100-$n)) > /tmp/2d.c.$n ; done
> (with Kernel 3)
> $ for n in 100 200 300 400 500; do
> > ./a.out -n $n $((1100-$n)) > /tmp/2d.c.nodma.$n ; done
>
> The table below is the last numbers printed by the test program
> ((number of reads)/2 in 5 minutes). Clockpro (with or without the
> ZONE_DMA modification) is always slower with one exception, and
> the slowdown can be as large as 42-54%.
>
> I've put the complete data and some generated figures at
> http://people.valinux.co.jp/~iwamoto/clockpro-20051231/
>
> n Kernel 1 Kernel 2 Kernel 3
> ======================================
> 100 373600 298720 395818
> 200 385639 272749 272166
> 300 371047 243734 262370
> 400 367691 213974 169714
> 500 147130 126284 103038

Great test case, I'll run this on my latest code and look into this.
Thanks for the effort.

As for the lapping of the hands, I'll have to get back to you on that
one. The way I understood the algorithm it is perfectly fine for the
hands to lap. I'll try and express my understanding in a later mail.

Kind regards,
Peter