Re: [PATCH] cat, cp, mv, install, split: Set the minimum IO block size used, to 64KiB

[Bernhard Voelker]

On 07/21/2011 03:59 PM, Pádraig Brady wrote:
> On 21/07/11 13:15, Bernhard Voelker wrote:
> > On 07/21/2011 02:06 PM, Bernhard Voelker wrote:
> > > On 07/21/2011 01:21 PM, Pádraig Brady wrote:
> > > > I'm a little wary of this being too aggressive,
> > > > but it does give a noticeable (13%) boost on my new laptop.
> > > > Here are the numbers from dd bs=$blksize if=/dev/zero of=/dev/null
> > > >
> > > > blksize system-1 system-2
> > > > ----------------------------
> > > > 1024 734 MB/s 1.7 GB/s
> > > > 2048 1.3 GB/s 3.0 GB/s
> > > > 4096 2.4 GB/s 5.1 GB/s
> > > > 8192 3.5 GB/s 7.3 GB/s
> > > > 16384 3.9 GB/s 9.4 GB/s
> > > > 32768 5.2 GB/s 9.9 GB/s
> > > > 65536 5.3 GB/s 11.2 GB/s
> > > > 131072 5.5 GB/s 11.8 GB/s
> > > > 262144 5.7 GB/s 11.6 GB/s
> > > > 524288 5.7 GB/s 11.4 GB/s
> > > > 1048576 5.8 GB/s 11.4 GB/s
> > >
> > > Hmm, I've taken the script from the test, but I'm not
> > > quite sure about the numbers on my system:
> > >
> > > $ for i in $(seq 0 10); do bs=$((1024*2**$i)); printf "%7s=" $bs;
> > > src/timeout --foreground -sINT 1 dd bs=$bs if=/dev/zero of=/dev/null
> > > 2>&1 | sed -n 's/.* \([0-9.]* [GM]B\/s\)/\1/p' ; done
> > > 1024=2.3 GB/s
> > > 2048=4.0 GB/s
> > > 4096=6.7 GB/s
> > > 8192=9.7 GB/s
> > > 16384=16.3 GB/s
> > > 32768=31.3 GB/s
> > > 65536=52.2 GB/s
> > > 131072=81.6 GB/s
> > > 262144=115 GB/s
> > > 524288=141 GB/s
> > > 1048576=157 GB/s
> > >
> > > I have a "Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz" system.
> > > And I used `src/timeout` from the latest `git pull`.
>
> Wow, what?
> Total guess. Perhaps your hardware has facilities to allow the kernel
> determine the buffers haven't been modified, thus avoiding
> the data copy in the write to /dev/null ??
> What kernel are you using?

genuine OpenSuSE 11.4: kernel 2.6.37.6-0.5-desktop,

> Mine is 2.6.38.8-34.fc15.x86_64.
> I wonder do the iflag=nocache oflag=nocache params change things?

nope:

for i in $(seq 0 15); do bs=$((1024*2**$i)); printf "%8s=" $bs; 
src/timeout --foreground -sINT 1 src/dd bs=$bs iflag=nocache 
oflag=nocache  if=/dev/zero of=/dev/null 2>&1  | sed -n 's/.* \([0-9.]* 
[GM]B\/s\)/\1/p' ; done
    1024=1.8 GB/s
    2048=2.8 GB/s
    4096=4.2 GB/s
    8192=6.9 GB/s
   16384=12.0 GB/s
   32768=22.5 GB/s
   65536=40.0 GB/s
  131072=65.8 GB/s
  262144=96.4 GB/s
  524288=128 GB/s
 1048576=150 GB/s
 2097152=162 GB/s
 4194304=171 GB/s
 8388608=175 GB/s
16777216=175 GB/s
33554432=176 GB/s

> > The situation changes when I specify ibs and obs for dd
> > (I looped until 15) for testing):
> >
> > berny@blackice:~/git/coreutils>  for i in $(seq 0 15); do
> > bs=$((1024*2**$i)); printf "%8s=" $bs; src/timeout --foreground -sINT 1
> > src/dd ibs=$bs obs=$bs if=/dev/zero of=/dev/null 2>&1  | sed -n 's/.*
> > \([0-9.]* [GM]B\/s\)/\1/p' ; done
> >      1024=1.9 GB/s
> >      2048=3.0 GB/s
> >      4096=4.5 GB/s
> >      8192=5.9 GB/s
> >     16384=7.2 GB/s
> >     32768=7.8 GB/s
> >     65536=8.7 GB/s
> >    131072=9.3 GB/s
> >    262144=9.6 GB/s
> >    524288=9.8 GB/s
> >   1048576=9.9 GB/s
> >   2097152=6.0 GB/s
> >   4194304=5.1 GB/s
> >   8388608=4.6 GB/s
> > 16777216=4.4 GB/s
> > 33554432=4.3 GB/s
>
> So you get more "standard" results with the data copy,
> with a corresponding 11.5% increase when going from 32K ->  64K.
> Interestingly, you only see a drop in performance at 1M ->  2M,
> whereas I gradually drop performance starting at 64K ->  32K.
>
>      1024=1.5 GB/s
>      2048=2.7 GB/s
>      4096=4.3 GB/s
>      8192=5.9 GB/s
>     16384=6.1 GB/s
>     32768=5.9 GB/s
>     65536=6.4 GB/s
>    131072=6.1 GB/s
>    262144=5.2 GB/s
>    524288=4.2 GB/s
>   1048576=4.3 GB/s
>   2097152=4.2 GB/s
>   4194304=3.4 GB/s
>   8388608=3.3 GB/s
> 16777216=3.4 GB/s
> 33554432=3.4 GB/s

Do you think that the assumption - that the io block size of
a sample dd run can be transfered to cat, cp et al - is valid?

Have a nice day,
Berny