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Re: [PATCH] cat, cp, mv, install, split: Set the minimum IO block size u


From: Pádraig Brady
Subject: Re: [PATCH] cat, cp, mv, install, split: Set the minimum IO block size used, to 64KiB
Date: Thu, 21 Jul 2011 14:59:56 +0100
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.8) Gecko/20100227 Thunderbird/3.0.3

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

> The situation changes when I specify ibs and obs for dd
> (I looped until 15) for testing):
> 
> address@hidden:~/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

cheers,
Pádraig.



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