Re: [Lse-tech] Re: Preliminary results of using multiblock raw I/O

Jens Axboe
2001-10-23T18:10:05Z

On Tue, Oct 23 2001, Shailabh Nagar wrote:
> >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.
>
> The patch below attempts to address exactly that - reducing the number of
> submit_bh/__make_request() calls made for raw I/O. The basic idea is to do
> a major
> part of the I/O in page sized blocks.
>
> Comments on the idea ?

Looks fine to me.

--
Jens Axboe