[linux-cifs-client] extremely slow throughput writing to remote shares

[Steven French]

My experiments with cifs writing over gigabit showed reasonable utilization
but would be much better with a rewrite of the cifs_writepages code to
allow more async/parallelized write.   cifs now defaults to sequnetial 52K
writes, a large enough size, but unless the copy application is
multithreaded, the latency between server response and tcp acks dominates
(since the writes are not parallelized from a single threaded copy
application).    There is some proposed work to make this more async which
would help.

The cifs improvement (around 2.6.15) for using iovecs on write (which
eliminated a large memory allocation on the client, which could sometimes
cause delays while the client mm hunted for eight free contiguous pages)
also helps.


Steve French
Senior Software Engineer
Linux Technology Center - IBM Austin
phone: 512-838-2294
email: sfrench at-sign us dot ibm dot com

linux-cifs-client-bounces+sfrench=us.ibm.com at lists.samba.org wrote on
05/22/2006 08:19:35 AM:

> Hi all!
>
> I regularly need to copy a bunch of large files (~150MB-1GB) to a CIFS
> share (on a samba server). The machines are connected by a
> consumer-grade Gbit network, which get ~540mbps in NPtcp and nearly
> that on FTP transfers (as long as the files fit in the destination's
> cache).
>
> Problem is, the cifs performance is horrible. I get a little under
> 6MB/s, which is not quite the sustained writing speed of the target
> disk's RAID-5 (8 MB/s). This leads me to believe that the recieving
> side does not cache or is forced to sync continually.
>
> Just to rule out the samba server I mounted a Windows (XPsp2) share
> the same way, and it behaves likewise: 14MB/s (sustained write of the
> disk a little over 20MB/s)
>
> Tested by copying a 512MB test file (dded from /dev/zero), that was
> bound to fit in cache.
>
> In the past I've used gnome-vfs to do the copying, but testing was
> done with mount -t cifs. No change with mount -t smbfs, if there even
> is a difference.
>
> Copying to the same server(s) from Windows clients is fine.
>
> I can't offer any hints as to when it broke, I recently had to replace
> the motherboard and NIC of the machine, along with an update of Debian
> testing.
>
> Both server and client use samba packages version 3.0.22-1 (probably
> those aren't even involved), the client has the stock Debian testing
> kernel (2.6.15 atm)
>
> Thanks,
>
> C.
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