From: Paolo Ornati <ornati@lycos.it>
To: Ed Sweetman <ed.sweetman@wmich.edu>
Subject: Re: Strange IDE performance change in 2.6.1-rc1 (again)
Date: Fri, 2 Jan 2004 22:04:27 +0100
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On Friday 02 January 2004 19:08, Ed Sweetman wrote:
>
>
> Note, sometimes when moving backwards back to a lower readhead my speed
> does not decrease to the values you see here. readahead on my system
> always goes up (on avg) with higher readahead numbers, maxing at 8192.
> No matter the buffer size or speed or position the ide drive is in.
>
> hdparm -t is difficult to get really accurate, which is why they suggest
> running it multiple times.  I see differences of 4MB/sec on subsequent
> runs without changing anything.  run hdparm -t at least 3-4 times for
> each readahead value.
>
> I suggest trying 128, 256,512,8192 as values for readahead and skip all
> those crap numbers in between.
>
>
> if you still see on avg lower numbers on the top end, try nicing hdparm
> to -20.  Also, update to a newer hdparm. hdparm v5.4, you seem to be
> using an older one.
>

ok, hdparm updated to v5.4

and this is the new script:
_____________________________________________________________________
#!/bin/bash

# This script assumes hdparm v5.4

NR_TESTS=3
RA_VALUES="64 128 256 8192"

killall5
sync
hdparm -a 0 /dev/hda > /dev/null
hdparm -t /dev/hda > /dev/null

for ra in $RA_VALUES; do
    hdparm -a $ra /dev/hda > /dev/null;
    echo -n $ra$'\t';
    tot=0;
    for i in `seq $NR_TESTS`; do
	tmp=`nice -n '-20' hdparm -t /dev/hda|grep 'Timing'|tr -d ' '|cut -d'=' -f2|cut -d'M' -f1`;
	tot=`echo "scale=2; $tot+$tmp" | bc`;
    done;
    s=`echo "scale=2; $tot/$NR_TESTS" | bc`;
    echo $s;
done
_____________________________________________________________________


The results are like the previous.

2.6.0:
64        31.91
128      31.89
256      26.22	# during the transfer HD LED blinks
8192    26.26	# during the transfer HD LED blinks

2.6.1-rc1:
64        25.84	# during the transfer HD LED blinks
128      25.85	# during the transfer HD LED blinks
256      25.90	# during the transfer HD LED blinks
8192    26.42	# during the transfer HD LED blinks

I have tried with and without "nice -n '-20'" but without any visible changes.

Performance with 2.4:
with kernel 2.4.23 && readahead = 8 I get 31.89 MB/s...
changing readahead doesn't seem to affect the speed too much.

Bye

-- 
	Paolo Ornati
	Linux v2.4.23

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