linux-kernel - Re: high system cpu load during intense disk i/o

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Message-ID: <46B7C18E.1050008@gmx.net>
Date:	Tue, 07 Aug 2007 02:49:18 +0200
From:	Dimitrios Apostolou <jimis@....net>
To:	Rafał Bilski <rafalbilski@...eria.pl>
CC:	linux-kernel@...r.kernel.org
Subject: Re: high system cpu load during intense disk i/o

Rafał Bilski wrote:
>> Hello Rafal,
> Hello,
>> However I find it quite possible to have reached the throughput limit 
>> because of software (driver) problems. I have done various testing 
>> (mostly "hdparm -tT" with exactly the same PC and disks since about 
>> kernel 2.6.8 (maybe even earlier). I remember with certainty that read 
>> throughput the early days was about 50MB/s for each of the big disks, 
>> and combined with RAID 0 I got ~75MB/s. Those figures have been 
>> dropping gradually with each new kernel release and the situation 
>> today, with 2.6.22, is that hdparm gives maximum throughput 20MB/s for 
>> each disk, and for RAID 0 too!
> Just tested (plain curiosity).
> via82cxxx average result @533MHz:
> /dev/hda:
> Timing cached reads:   232 MB in  2.00 seconds = 115.93 MB/sec
> Timing buffered disk reads:   64 MB in  3.12 seconds =  20.54 MB/sec
> pata_via average result @533MHz:
> /dev/sda:
> Timing cached reads:   234 MB in  2.01 seconds = 116.27 MB/sec
> Timing buffered disk reads:   82 MB in  3.05 seconds =  26.92 MB/sec

Interesting! I haven't tried libata myself on that system, I only have 
remote access to it so I'm a bit afraid...

Rafal, I hope that system you run hdparm on isn't the archlinux one! Is 
it easy to load an old kernel (even two years old) and do the same test? 
If it is, please let me know of the results.


Thanks in advance,
Dimitris


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