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Subject(reiserfs) Re: More on 2.2.18pre2aa2
On Tue, 12 Sep 2000, Rik van Riel wrote:

>But you don't. Transfer rate is very much dependant on the
>kind of load you're putting on the disk...

Transfer rate means `hdparm -t` in single user mode. Try it and you'll see
you'll get always the same result.

>Throughput really isn't that relevant here. The problems are

Thoughput is relevant. Again, how do you get a 1msec latency out of a
blockdevice that writes 1 request every two seconds?

>With equally horrible results for most machines I've
>seen. For a while I actually thought the bug /must/
>have been somewhere else because I saw processes
>'hanging' for about 10 minutes before making progress
>again ...

As said in my earlier email the current 2.4.x elevator scheduler is
_disabled_. I repeat: you should change include/linux/elevator.h and set
the read and write latency to 250 and 500 respectively. You won't get
latency as good as in test1, but it won't hang for 10 minutes.

I and Jens sent a patch to Linus to reenable that push fixing some other
problem of the blkdev merging reported by Giuliano Pochini, plus wake-one
flow control, plus I fixed the DMA_CHUNK_SIZE thing that was buggy and
it's still buggy in the sparc64 case (I didn't fixed sparc64 in my patch,
the DMA_CHUNK_SIZE should limit the segments to
max(64,SHpnt->sg_tablesize) and not to 64 as now), plus it allowed 512K
sized SCSI commands, plus some other minor thing but it didn't get merged.

>Not really. What about just using something like
>"half a second, but at least 10 requests liberty to
>reorder" ?

I doesn't make sense.

Andrea


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