Translation:The performance of this computer is better than the performance of my computer.
Speaking of computers, the plural seems preferable, but the singular exists as well, especially in non-technical contexts: הָרַעֲיוֹן נָאֶה אֲבָל בִּצוּעַ אֵינוֹ קַל "The idea is fine, but the execution is not easy" or הַבִּצוּעַ הַמּוּסִיקָלִי שֶׁלוֹ טוֹב "his musical performance is good".
(Millallero) קמילה, in my opinion that is not idiomatic English in this context. Assessing a computer's overall performance (or, for that matter, an employee's job performance) is a single assessment even though it may be based on multiple criteria and multiple events.
My main association with the plural "performances" is with multiple presentations of a show (stage or screen) or other artistic event.