Stevie P wrote: > I've been having this problem too on Ubuntu 12.04, but I think I've got > to the bottom of it. > > Using the ss utility with -m shows that the write buffer is limited to > 68KB. The Linux stack is measuring the link speed at 2-4Mbps, which > should be enough. However, with roughly 60-70ms RTT latency (it's over > wireless), and with such a small buffer, keeping a steady flow of data > to the Squeezebox requires the buffer to be constantly topped up. This > is not possible in spotifyd, because the libspotify code tends to block > for roughly 190ms at a time in the same thread that sends data to the > Squeezebox. Consequently, the slightest hiccup in the wireless link will > cause the drop-outs we've been experiencing. > > I've tried playing about with the TCP buffer tunings, but it now appears > that this won't work because spotifyd calls setsockopt to set the send > buffer size to 32768 (which the Linux stack doubles to 65536 to cover > overheads) and this effectively switches off the write buffer autotuning > processing. > > As an experiment I've made the following changes. > > 1. Changed the net.core.wmem_max setting from the rather low default > value of 131072 to 12582912. > 2. Modified spotifyd64 with hexedit to call setsockopt with a value of > 8388608. > > The result of these changes is that the plugin is now quite happily > streaming to the Squeezebox without drop-outs. > > Three potential solutions spring to mind. > > 1. Move the send processing to another thread. (Complex, but requires no > network buffer tuning whatsoever) > 2. Specify a much larger buffer size in setsockopt (Easy, requires only > net.core.wmem_max to be changed) > 3. Don't call setsockopt at all (Easy, but requires user changes of > net.core.wmem_max and net.ipv4.tcp_wmem. > > Given the asymmetrical profile of data being sent to and from the > Squeezebox, it might also help to call setsockopt to set TCP_NODELAY on > the socket in order to disable the Nagle algorithm if that isn't already > done. > > I hope this is of some use.
Hi - I can definitely avoid calling setsockopt - it is there to make the buffer larger than default on windows and old linux version which default to smaller versions. As you have diagnosed spotifyd is currently using the tcp send buffer as the main buffer for the stream. It tries to write to it whenever the callback from libspotify calls it with data and if it can't write to the socket then buffers it. However it won't try to write again until libspotify calls it again. This clearly means that it requires regular calls from libspotify and also a large enough buffer and in the tcp send buffer. This was all working ok until something changed in linux... Anyway let me look at whether another thread would be trivial or whether buffer tuning and not calling setsockopt is the easiest thing to do. ------------------------------------------------------------------------ Triode's Profile: http://forums.slimdevices.com/member.php?userid=17 View this thread: http://forums.slimdevices.com/showthread.php?t=97851 _______________________________________________ plugins mailing list plugins@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/plugins
