Messages in this thread | | | Date | Mon, 9 Apr 2001 02:13:09 +0200 | From | Andi Kleen <> | Subject | Re: Zero Copy IO |
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On Sun, Apr 08, 2001 at 04:31:27PM -0700, Alex Q Chen wrote: > I am trying to find a way to pin down user space memory from kernel, so > that these user space buffer can be used for direct IO transfer or > otherwise known as "zero copying IO". Searching through the Internet and > reading comments on various news groups, it would appear that most > developers including Linus himself doesn't believe in the benefit of "zero > copying IO". Most of the discussion however was based on network card > drivers. For certain other drivers such as SCSI Tape driver, which need to > handle great deal of data transfer, it would seemed still be more > advantageous to enable zero copy IO than copy_from_user() and copy_to_user > () all the data. Other OS such as AIX and OS2 have kernel functions that > can be used to accomplish such a task. Has any ground work been done in > Linux 2.4 to enable "zero copying IO"?
Yes, e.g. the raw io device does it using kiovecs. See drivers/char/raw.c,fs/iobuf.c et.al. 2.4+zerocopy networking also has a different implementation. The raw.c implementation is not very efficient at the moment though, mostly because of limitations in the block device layer (but that should be no problem for a direct tape driver) This work is also in the 2.2 kernels of most distributions.
-Andi
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