lkml.org 
[lkml]   [2001]   [Oct]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [Lse-tech] Re: Preliminary results of using multiblock raw I/O
On Tue, Oct 23 2001, Martin Frey wrote:
> >I haven't seen the SGI rawio patch, but I'm assuming it used kiobufs to
> >pass a single unit of 1 meg down at the time. Yes currently we do incur
> >significant overhead compared to that approach.
> >
> Yes, it used kiobufs to get a gatherlist, setup a gather DMA out
> of that list and submitted it to the SCSI layer. Depending on
> the controller 1 MB could be transfered with 0 memcopies, 1 DMA,
> 1 interrupt. 200 MB/s with 10% CPU load was really impressive.

Let me repeat that the only difference between the kiobuf and the
current approach is the overhead incurred on multiple __make_request
calls. Given the current short queues, this isn't as bad as it used to
be. Of course it isn't free, though.

It's still 0 mem copies, and can be completed with 1 interrupts and DMA
operation.

--
Jens Axboe

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

\
 
 \ /
  Last update: 2005-03-22 13:10    [W:0.093 / U:0.116 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site