[kio] [Bug 291835] KIO very slow when copying from network through smb

[Dawit Alemayehu]

https://bugs.kde.org/show_bug.cgi?id=291835

--- Comment #33 from Dawit Alemayehu <adawit at kde.org> ---
(In reply to comment #31)
> Well, i just checked your commit again. It doubles the transfer speed in my
> case, which is nice.
> The increased buffer size wasn't mentioned in the comment, so i guess nobody
> saw it.
> 
> However, using cifs, transfer speed is still twice as high as using kio-smb
> with the 64k buffer size, because it requests more data before a reply comes
> in (async read-ahead, i think it's in file.c: cifs_readpages).
> And for some reason, the kio-slave does that too if buffer size is increased
> above the 64k, thats why a buffer size of 1048576 works better, even if the
> transferred packets are only allowed to be 64k.

1048576 is default read/write size for SMB2 protocol. See the smb.conf man
pages or the excerpt taken from those pages at
https://lists.samba.org/archive/samba-technical/2011-June/078093.html for the
details. The newer CIFS protocol implementations support large transfer sizes
beyond 65K. However, kio_smb cannot simply hard code and use such large buffer
size because it has to support severs that implement the older version of the
protocol. And hard coding such change will likely impact those servers
adversely.

> So beyond buffer size increase (which is nice!), read-ahead would be useful
> to reduce waiting time.

No there is a much easier solution to this and that is to do the same thing the
command line smbclient does. By default, smbclient sets the io buffer size to
64512 (ctx->io_bufsize = 64512). However, you can override that value using a
command line option (-b). We can provide the same configuration such that
people can set the read/write or general buffer size globally or per specific
hosts in kio_smbrc. The default will still be 64K, but the user can change that
value to their heart's content.

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