> -----Original Message----- > From: linux-cifs-owner@xxxxxxxxxxxxxxx [mailto:linux-cifs- > owner@xxxxxxxxxxxxxxx] On Behalf Of Dave Chiluk > Sent: Wednesday, February 27, 2013 5:44 PM > To: Steve French > Cc: Jeff Layton; Stefan (metze) Metzmacher; Dave Chiluk; Steve French; > linux-cifs@xxxxxxxxxxxxxxx; samba-technical@xxxxxxxxxxxxxxx; linux- > kernel@xxxxxxxxxxxxxxx > Subject: Re: [PATCH] CIFS: Decrease reconnection delay when switching nics > > On 02/27/2013 04:40 PM, Steve French wrote: > > On Wed, Feb 27, 2013 at 4:24 PM, Dave Chiluk > <dave.chiluk@xxxxxxxxxxxxx> wrote: > >> On 02/27/2013 10:34 AM, Jeff Layton wrote: > >>> On Wed, 27 Feb 2013 12:06:14 +0100 > >>> "Stefan (metze) Metzmacher" <metze@xxxxxxxxx> wrote: > >>> > >>>> Hi Dave, > >>>> > >>>>> When messages are currently in queue awaiting a response, decrease > >>>>> amount of time before attempting cifs_reconnect to SMB_MAX_RTT > = > >>>>> 10 seconds. The current wait time before attempting to reconnect > >>>>> is currently 2*SMB_ECHO_INTERVAL(120 > >>>>> seconds) since the last response was recieved. This does not take > >>>>> into account the fact that messages waiting for a response should > >>>>> be serviced within a reasonable round trip time. > >>>> > >>>> Wouldn't that mean that the client will disconnect a good > >>>> connection, if the server doesn't response within 10 seconds? > >>>> Reads and Writes can take longer than 10 seconds... > >>>> > >>> > >>> Where does this magic value of 10s come from? Note that a slow > >>> server can take *minutes* to respond to writes that are long past the > EOF. > >> It comes from the desire to decrease the reconnection delay to > >> something better than a random number between 60 and 120 seconds. I > >> am not committed to this number, and it is open for discussion. > >> Additionally if you look closely at the logic it's not 10 seconds per > >> request, but actually when requests have been in flight for more than > >> 10 seconds make sure we've heard from the server in the last 10 seconds. > >> > >> Can you explain more fully your use case of writes that are long past > >> the EOF? Perhaps with a test-case or script that I can test? As far > >> as I know writes long past EOF will just result in a sparse file, and > >> return in a reasonable round trip time *(that's at least what I'm > >> seeing with my testing). dd if=/dev/zero of=/mnt/cifs/a bs=1M > >> count=100 seek=100000, starts receiving responses from the server in > >> about .05 seconds with subsequent responses following at roughly > >> .002-.01 second intervals. This is well within my 10 second value. > > > > Note that not all Linux file systems support sparse files and > > certainly there are cifs servers running on operating systems other > > than Linux which have popular file systems which don't support sparse > > files (e.g. FAT32 but there are many others) - in any case, writes > > after end of file can take a LONG time if sparse files are not > > supported and I don't know a good way for the client to know that > > attribute of the server file system ahead of time (although we could > > attempt to set the sparse flag, servers can and do lie) > > > > It doesn't matter how long it takes for the entire operation to complete, just > so long as the server acks something in less than 10 seconds. Now the > question becomes, is there an OS out there that doesn't ack the request or > doesn't ack the progress regularly. SMB/CIFS servers will signal the operation "going async" by returning a STATUS_PENDING response if the operation is not prompt, but this only happens once. The client is still expected to run a timer, and recover from possibly lost responses and/or unresponsive servers. Windows clients extend their timeout when this occurs, typically quadrupling it. Some clients will issue ECHO requests to probe the server in this case, but it is neither a protocol requirement nor does it truly address the issue of tracking each pending operation. Windows SMB2 clients do not do this. -- To unsubscribe from this list: send the line "unsubscribe linux-cifs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
