* REQ_HARDBARRIER and REQ_SOFTBARRIER
@ 2007-02-24 9:56 V P
2007-02-24 12:42 ` Jens Axboe
0 siblings, 1 reply; 2+ messages in thread
From: V P @ 2007-02-24 9:56 UTC (permalink / raw)
To: linux-kernel
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
it a must for a request to have this? Can I reorder two requests with
these flags set? How is SOFTBARRIER different from HARDBARRIER?
I appreciate your time and help.
Thanks much.
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: REQ_HARDBARRIER and REQ_SOFTBARRIER
2007-02-24 9:56 REQ_HARDBARRIER and REQ_SOFTBARRIER V P
@ 2007-02-24 12:42 ` Jens Axboe
0 siblings, 0 replies; 2+ messages in thread
From: Jens Axboe @ 2007-02-24 12:42 UTC (permalink / raw)
To: V P; +Cc: linux-kernel
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
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