[SCM] Samba Shared Repository - branch v3-2-test updated - initial-v3-2-test-2626-g719527f

David Collier-Brown davecb at sun.com
Fri Feb 29 15:57:03 GMT 2008

Volker Lendecke wrote:
> static int io_bufsize = 64512;
> With this setting we would loose most of what that patch
> does, that's why I'm hard-coding that 1024*1024 bufsize in
> the call to cli_pull in do_get. If we had a default of 64k
> read window then we would not gain anything from parallel
> reads. With this change I anyhow doubt that the huge buffer
> sizes gain more than just some very few percent, I would be
> very surprised if it gains anything at all on gigabit
> ethernet. 10gig ethernet might be different though.
> io_bufsize here is very similar to the TCP window size, and
> on fast networks you don't get very far with 64k.

  In tests with both ufs and qfs many moons ago, we found that
the speed *leaped* up for large files and large read sizes: 
gifs attached.

> We could pass io_bufsize to cli_pull, but then I would
> really like to increase the default value of io_bufsize to
> at least half a meg.

Big buffers only *start* helping at 64 KB.  Large is good,
and it's especially good if the read size is bigger than the 
file (;-)) 

The reason they help independent of the network speed
is that large reads and writes trigger both read ahead
add I/O coalescing, which work together to produce
and M * M kind of an improvement.


David Collier-Brown            | Always do right. This will gratify
Sun Microsystems, Toronto      | some people and astonish the rest
davecb at sun.com                 |                      -- Mark Twain
(905) 943-1983, cell: (647) 833-9377, home off: (416) 223-5943 
(800) 555-9786 x56583, bridge: (877) 385-4099 code: 506 9191#
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