In my mind, one of the most stunning parallels between Sri Lanka and Rwanda is how the world is silent in both settings. There might be some outcry or some criticism from the outside world but very little seems to be present. The situation in Rwanda happened mostly outside the reaction of the world, and while condemnation was swift, little was done to stop the murdering of innocent civilians: There was an international condemnation after the fact but little done to stop what was going on.
For the most part, there is also little world outcry in Sri Lanka. Little, if any, attention is paid to what is happening there. In Sri Lanka, the Sinhalese and Tamils are engaged in a similar pattern of destruction and "genocidal character" that is present in Rwanda. World silence is present in both conditions. Both settings feature groups using political power to advance their own sectarian agenda.
I think that a significant difference would be the duration of the killings. Sri Lanka's trouble have been ongoing since the early 1980s, while Rwanda's genocide took place in a period of only about 100 days. Sri Lanka's violence has also taken on many forms in terms of terrorist attacks, small scale violence between both sides, and other forms of violence that lie represent a protracted conflict being present. Rwanda's genocide was much more forceful in nature, consisting of one group wiping out another group of people en masse and without much by way of small scale measures. The mere idea of wiping out over a million people in a few months is uniquely different from the death and murder in Sri Lanka.