On 09/04/2009 01:58 PM, Trond Myklebust wrote:
On Sep 4, 2009, at 16:49, Ben Greear <greearb@xxxxxxxxxxxxxxx> wrote:
I'm using O_DIRECT (so that the server is continually stressed even if
the file would have otherwise been cached locally on the client).
This still causes a copy of the contents to user-space when I do a
read() call though, as far as I can tell. Since I'm normally not looking
at this data at all, the memory copy from kernel to user is wasted
effort in my case.
You're missing the point. O_DIRECT does not copy data from the kernel
into userspace. The data is placed directly into the user buffer from
the socket.
I may be going about things all wrong...
The only faster alternative would be to directly discard the data in the
socket, and we offer no option to do that.
I'm opening an fd like this:
uint32 flgs = O_RDONLY | O_DIRECT | O_LARGEFILE;
fd = open(fname, flgs);
Then read from the fd it:
int retval = read(fd, rcv_buffer_ptr, my_read_len);
rcv_buffer_ptr is just a 1MB (or so) array of bytes.
Maybe I need to use aio_read with O_DIRECT to get the benefits you speak of?
Thanks,
Ben
--
Ben Greear <greearb@xxxxxxxxxxxxxxx>
Candela Technologies Inc http://www.candelatech.com
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