Rashi, from Pesachim 117a: We read this like 'Kol Elu.' The entire Sefer is called on David's name, even what is attributed to Bnei Korach and 10 Chachamim (refer to 1:1:1:1-2), for he is called "Ne'im Zemiros Yisrael" (Shmuel II, 23:1).

Rashi: It means 'finished.' This Mizmor was not written in the proper place; the Sefer is not in chronological order. David said this in his old age, when he made Shlomo king. Malbim - it was his last Tefilah after anointing Shlomo.

Radak: If this Mizmor refers to Shlomo, I explained this above (refer to 72:1:1:3).

Radak citing his father: If this Mizmor refers to Mashi'ach, when these consolations will be fulfilled, David's Tefilos will be finished. It does not say that his Zemiros or praises will be finished, rather, Tefilos for Kaparah or salvation. When Yisrael will leave Galus and be in their land and Mashi'ach ben David will rule over them, they will not need Kaparah, salvation or success; they will have everything.