Re: Process Scheduling Issue using sg/libata

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Fajun Chen wrote:
..
I verified your program works in my system and my application works as
well if changed accordingly. However, this change (indirect IO in sg
term) may come at a performance cost for IO intensive applications
since it does NOT utilize mmaped buffer managed by sg driver.  Please
see relevant sg document below:
http://sg.torque.net/sg/p/sg_v3_ho.html#id2495330
http://sg.torque.net/sg/p/sg_v3_ho.html#dmmio
As an example, sg_rbuf.c in sg3_util package uses SG_FLAG_MMAP_IO flag
in SG_IO. Please see source code attached. I also noticed that
MAP_ANONYMOUS is NOT used in mmap() call in sg_rbuf.c, which may not
be desirable as you pointed out in previous emails. So this brings up
an interesting sg usage issue: can we use MAP_ANONYMOUS with
SG_FLAG_MMAP_IO flag in SG_IO?
..

The SG_FLAG_MMAP works only with /dev/sg* devices, not /dev/sd* devices.
I don't know which kind you were trying to use, since you still have
not provided your source code for examination.

If you are using /dev/sg*, then you should be able to get your original mmap()
code to work.  But the behaviour described thus far seems to indicate that
your secret program must have been using /dev/sd* instead.

Cheers
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