cvs commit: src/tools/regression/bin/mv regress.sh

[Diomidis Spinellis]

Pawel Jakub Dawidek wrote:
> On Mon, Mar 17, 2008 at 05:24:00PM +0200, Diomidis Spinellis wrote:
>> Pawel Jakub Dawidek wrote:
>>> I was thinking about adding two options to cp(1) (-1 and -2) to give
>>> cp(1) a hint if the copy is done inside one disk or between separate
>>> disks. In -1 case cp(1) will read as large blocks as possible and then
>>> write them, in -2 case it will spawn two threads: one reader and one
>>> writer working in parallel. Performance improvements are very visible
>> >from what I tested.
>> Adding hints to cp(1) hinders portability.  Even on the same OS, if two 
>> systems have their disks differently configured, a script may end up 
>> with an inappropriate hint on one of the two.  Why not use fstat(2) to 
>> automatically determine if the file resides on different disks, and act 
>> accordingly?
> 
> You can't say if this is the same disk or not. Think about more complex
> situations like partitions on RAIDs, etc.


(Or, even worse, volumes spanning multiple disks).  What if cp(1) always 
worked in multithread mode for large files.  Is that a pessimization for 
copies on the same disk?  Don't disk accesses get appropriately 
reordered lower down?

-- 
Diomidis Spinellis - http://www.spinellis.gr