Reading the patch, it sounds like a better set of parameters to try would be: vm.dirty_background_ratio=10 vm.dirty_bytes=90
Cheers, wad On May 11, 2010, at 10:41 PM, James Cameron wrote: > On Tue, May 11, 2010 at 10:16:13PM -0400, Martin Langhoff wrote: >> What you are saying is that this is a different issue from what dsd >> tracked down -- entirely possible that these are 2 orthogonal issues. > > Yes, entirely possible. > >> Does the frequency and/or std deviation change if you tweak the >> vm.dirty_* sysctl values? > > Yes, significantly. What I've observed is most likely entirely due to > vm.dirty_* behaviour. > > The default on os123 is > > vm.dirty_background_bytes=0 > vm.dirty_background_ratio=10 > vm.dirty_bytes=0 > vm.dirty_expire_centisecs=3000 > vm.dirty_ratio=20 > vm.dirty_writeback_centisecs=500 > > Changing this to > > vm.dirty_background_ratio=90 > vm.dirty_expire_centisecs=60000 > vm.dirty_ratio=90 > vm.dirty_writeback_centisecs=0 > > causes the dd to finish in 7 seconds instead of 92 seconds, the sync to > take much longer, and the write latencies are much smaller. > > So the effect I was seeing was documented ... "process which is > generating disk writes will itself start writing out dirty data.", per > vm.txt in Documentation/ > > -- > James Cameron > http://quozl.linux.org.au/ _______________________________________________ Devel mailing list [email protected] http://lists.laptop.org/listinfo/devel
