On Sep 4, 2009, at 17:12, Ben Greear <greearb@xxxxxxxxxxxxxxx> wrote:
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.
Use a (much) larger buffer. Linux clients are capable of reading 2MB
in a single RPC, so you won't be doing much in the way of parallel
reads with 1MB.
I'd also suggest bumping up the number of tcp slots (see in /proc/sys/
fs/nfs/). This should be done before you mount the NFS partition.
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