[6156] in linux-scsi channel archive
Re: how to get maximum datarate from SCSI
daemon@ATHENA.MIT.EDU (Doug Ledford)
Tue Mar 23 11:27:52 1999
Date: Tue, 23 Mar 1999 10:43:28 -0500
From: Doug Ledford <dledford@redhat.com>
To: Mateu Batle i Sastre <mbatle@iname.com>
CC: linux-scsi@vger.rutgers.edu
Mateu Batle i Sastre wrote:
>
> Hi everybody,
>
> I'm trying to get the maximum transfer datarate from several SCSI disks
> from a user application. I think the problem now is that all the transfers
> go through the buffer cache, which implies a lot of memory copy and this
> bounds the maximum I/O. It should be possible to access the SCSI disks
> bypassing the buffer cache of the block devices.
> Is there any easy way to do this ?
>
> My first option would be to use some special flag when openning the file
> to avoid going through the buffer cache. But I have not found anything
> similar.
>
> If not, I would have to modify the sd.c to to perform direct transfers
> without using the buffer cache.
Get Stephen Tweedie's current Raw I/O code and use that. It does
exactly what you are looking for. Unfortunately, the API to the code
will change in the future so it's an intermediate step right now and the
finished product will require some more code modifications on your part.
--
Doug Ledford <dledford@redhat.com>
Opinions expressed are my own, but
they should be everybody's.
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