From: Jens Axboe <axboe@suse.de>
To: Martin Frey <frey@scs.ch>
Cc: "'Shailabh Nagar'" <nagar@us.ibm.com>,
"'Reto Baettig'" <baettig@scs.ch>,
lse-tech@lists.sourceforge.net, linux-kernel@vger.kernel.org
Subject: Re: [Lse-tech] Re: Preliminary results of using multiblock raw I/O
Date: Tue, 23 Oct 2001 12:02:40 +0200 [thread overview]
Message-ID: <20011023120240.N638@suse.de> (raw)
In-Reply-To: <20011023084238.C638@suse.de> <000b01c15ba9$58ba4e90$e6c02f10@SCHLEPPDOWN>
In-Reply-To: <000b01c15ba9$58ba4e90$e6c02f10@SCHLEPPDOWN>
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
next prev parent reply other threads:[~2001-10-23 10:02 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-10-22 19:08 [Lse-tech] Re: Preliminary results of using multiblock raw I/O Shailabh Nagar
2001-10-23 6:42 ` Jens Axboe
2001-10-23 9:59 ` Martin Frey
2001-10-23 10:02 ` Jens Axboe [this message]
2001-10-23 16:23 ` Alan Cox
2001-10-23 17:49 ` Jens Axboe
2001-10-23 18:04 ` Alan Cox
-- strict thread matches above, loose matches on Subject: below --
2001-10-23 14:05 Shailabh Nagar
2001-10-23 14:12 Shailabh Nagar
2001-10-23 18:10 ` Jens Axboe
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