Messages in this thread | | | From | Arnd Bergmann <> | Subject | Re: Big I/O latencies, except when iotop is hooked | Date | Wed, 9 May 2012 20:43:11 +0000 |
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On Wednesday 09 May 2012, Felipe Contreras wrote: > And it doesn't tell me why I see the issue on my SSD as well; albeit > with much less delay. > > I'll try what you suggest, maybe I will get better performance by > aligning the partitions, but the real issue seems to lie elsewhere, > right?
For anything but the absolute worst devices, misaligning the partition should cause a linear increase in latency (maybe factor 2 in the worst case), so it doesn't explain the entire thing. However, you can use flashbench to find out the erase block size. If it's larger than 4MB, you definitely have a problem even with ext4 or btrfs. The latencies you get from garbage collection for a single write are roughly the time it takes to write one erase block, and that can be up to a second in the worst case (slow media with large erase blocks).
Arnd
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