Messages in this thread | | | Date | Sun, 6 Jan 2002 11:21:29 +0100 | From | Jens Axboe <> | Subject | Re: 2.5.2-pre performance degradation on an old 486 |
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On Sat, Jan 05 2002, Davide Libenzi wrote: > > > (*) 100MHz 486DX4, 28MB ram, no L2 cache, two old and slow IDE disks, > > > small custom no-nonsense RedHat 7.2, kernels compiled with gcc 2.95.3. > > > > Is this ISA (maybe it has something to do with ISA bouncing)? Mine is: > > > > 486 DX/2 ISA, Adaptec 1542, two slow scsi disks and a self-made > > slackware-based system. > > > > Can you also backout the scheduler changes to verify this? I have a > > backout patch for 2.5.2-pre6, if you don't want to do this for yourself. > > There should be some part of the kernel that assume a certain scheduler > behavior. There was a guy that reported a bad hdparm performance and i > tried it. By running hdparm -t my system has a context switch of 20-30 > and an irq load of about 100-110. > The scheduler itself, even if you code it in visual basic, cannot make > this with such loads. > Did you try to profile the kernel ?
Davide,
If this is caused by ISA bounce problems, then you should be able to reproduce by doing something ala
[ drivers/ide/ide-dma.c ]
ide_toggle_bounce() { ...
+ addr = BLK_BOUNCE_ISA; blk_queue_bounce_limit(&drive->queue, addr); }
pseudo-diff, just add the addr = line. Now compare performance with and without your scheduler changes.
-- Jens Axboe
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