Messages in this thread | | | Date | Tue, 23 Oct 2001 12:02:40 +0200 | From | Jens Axboe <> | Subject | Re: [Lse-tech] Re: Preliminary results of using multiblock raw I/O |
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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
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