Re: REQ_HARDBARRIER and REQ_SOFTBARRIER

[Jens Axboe]

On Sat, Feb 24 2007, V P wrote:
> Hi,
> 
> I'm trying to modify the ordering of I/O requests in Linux kernel, and
> came across the barrier flags REQ_HARDBARRIER and REQ_SOFTBARRIER.
> 
> One thing I noticed (which might be wrong) is that all the requests
> have both these flags set. What is the significance of these flags? Is

Uhm? That's definitely not true.

> it a must for a request to have this? Can I reorder two requests with
> these flags set? How is SOFTBARRIER different from HARDBARRIER?

Both imply a reordering barrier in the io scheduler, and the hard
barrier further implies a barrier at the drive/driver side. So you may
not reorder across a barrier.

-- 
Jens Axboe

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/