Messages in this thread | | | From | Marc-Christian Petersen <> | Subject | Re: 2.[45] fixes for design locking bug in wait_on_page/wait_on_buffer/get_request_wait | Date | Sat, 16 Nov 2002 18:23:26 +0100 |
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On Saturday 16 November 2002 17:59, Andrea Arcangeli wrote:
Hi Andrea,
> Your pausing problem have little to do with the pausing fix, the problem > for you is the read latency, you're not triggering the race condition > fixed by the pausing fix so it can't make differences. One of the > foundamental obstacles to the read latency is the size of the I/O queue, > factor that is workarounded by the read-latency patch that basically > bypasses the size of the queue hiding the problem and in turn can't fix > the write latency with O_SYNC and the read latency during true read aio > etc... ok, after some further tests, I think this is _somewhat_ FS dependent. I tried this with ext2, ext3 (no difference there) and also with ReiserFS and what must I say, those "Pausings" caused be the write latency doing it with ReiserFS are alot less than with ext2|ext3 but are still occuring.
There must went in something bullshitty into 2.4.19/2.4.20 that causes those ugly things because 2.4.18 does not have that problem. This is still why I don't use any kernels >2.4.18.
After changing elevator things like this:
root@codeman:[/] # elvtune /dev/hda
/dev/hda elevator ID 0 read_latency: 2048 write_latency: 1024 max_bomb_segments: 0
those "pausings" are less worse than before but are still there. NOTE: Write latency is lower than read latency (it's not a typo :)
ciao, Marc
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