bugThe GNU Hurd - Bugs: bug #17193, performance of `dd' w.r.t....


bug #17193: performance of `dd' w.r.t. different block sizes

Submitted by:  Thomas Schwinge <tschwinge>
Submitted on:  Mon Jul 24 14:44:01 2006  
Category: NoneSeverity: 3 - Normal
Priority: 5 - NormalItem Group: None
Status: NonePrivacy: Public
Assigned to: NoneOriginator Name: 
Open/Closed: OpenReproducibility: None
Size (loc): NonePlanned Release: None
Effort: 0.00
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Mon Jul 24 14:44:01 2006, original submission:

20:03 <antrik> with "dd if=/dev/hd0s6 of=/dev/hd0s8 bs=512" I get the same 20 kbyte/s as with cat
20:03 <antrik> but with bs=1k, I already get 75 k...
20:03 <antrik> 130 with 2k
20:04 <antrik> 230 with 4k
20:04 <antrik> and so on
20:04 <ness> Does copying the files stress ipc (I'd guess)?
20:05 <ness> Because overhead is smaller for larger payload sizes...
20:08 <antrik> well, with larger block sizes, the disk seeks considerably less; looks like each single copied block is written immediately...
20:09 <antrik> that doesn't explain the unexpected jump between 512 byte and 1024 byte block size, though
20:10 <antrik> maybe with 1024 it is fast enought so the disk access is optimized a bit at least, or something
20:11 <antrik> or it's some sheduling issue
20:27 <antrik> also, with sizes <512 there is no further slowdown
20:27 <antrik> (well, except when going <16...)
23:21 <antrik> interesting... if I give a larger blocksize to dd, the relative CPU consumption rises compared to that one of pflocal...
23:21 <antrik> and the CPU consumption of /dev/zero drops nearly to 0

Thomas Schwinge <tschwinge>
Project Administrator


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