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List:       linux-kernel
Subject:    Re: Where is the performance bottleneck?
From:       Holger Kiehl <Holger.Kiehl () dwd ! de>
Date:       2005-08-31 21:57:32
Message-ID: Pine.LNX.4.61.0508312148040.1081 () diagnostix ! dwd ! de
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On Thu, 1 Sep 2005, Nick Piggin wrote:

> Holger Kiehl wrote:
>
>> meminfo.dump:
>> 
>>    MemTotal:      8124172 kB
>>    MemFree:         23564 kB
>>    Buffers:       7825944 kB
>>    Cached:          19216 kB
>>    SwapCached:          0 kB
>>    Active:          25708 kB
>>    Inactive:      7835548 kB
>>    HighTotal:           0 kB
>>    HighFree:            0 kB
>>    LowTotal:      8124172 kB
>>    LowFree:         23564 kB
>>    SwapTotal:    15631160 kB
>>    SwapFree:     15631160 kB
>>    Dirty:         3145604 kB
>
> Hmm OK, dirty memory is pinned pretty much exactly on dirty_ratio
> so maybe I've just led you on a goose chase.
>
> You could
>    echo 5 > /proc/sys/vm/dirty_background_ratio
>    echo 10 > /proc/sys/vm/dirty_ratio
>
> To further reduce dirty memory in the system, however this is
> a long shot, so please continue your interaction with the
> other people in the thread first.
>
Yes, this does make a difference, here the results of running

   dd if=/dev/full of=/dev/sd?1 bs=4M count=4883

on 8 disks at the same time:

   34.273340
   33.938829
   33.598469
   32.970575
   32.841351
   32.723988
   31.559880
   29.778112

That's 32.710568 MB/s on average per disk with your change and without
it it was 24.958557 MB/s on average per disk.

I will do more tests tomorrow.

Thanks,
Holger

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