Toon van der Pas wrote:
>On Fri, Apr 18, 2003 at 01:45:36AM -0700, Andrew Morton wrote:
>
>>ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.5/2.5.67/2.5.67-mm4/
>>
>>. A bunch of anticipatory scheduler patches.
>>
>> For the first time ever, AS is working well with both IDE and SCSI
>> under all the usual tests.
>>
>> It works just fine on SCSI with zero TCQ tags, and with four TCQ tags.
>> At eight tags, read-vs-write performace is starting to measurably drop off.
>> At 32 tags it is about 2000x slower than at zero or four tags.
>>
>> My recommendation, as always, is to disable SCSI TCQ completely. If you
>> really must, set it to four tags.
>>
>
>What about drivers that bypass de SCSI layer?
>I administer a server with a Mylex RAID controller (DAC960)...
>
I'd say they will show the same behaviour. As far as we can tell
its an interaction between badly behaving TCQ disks (those which
allow lots of writes to bypass a read), and the anticipatory
scheduler. We will be working on fixing this so those inclined
can use huge numbers of outstanding tags without things going
too haywire.
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