The exclusive pion pair production cross-section in diffractive proton-proton collisions ($pp \to p \pi^+ \pi^- p$) was measured during the special low luminosity LHC runs at $\sqrt{s}=7$ TeV with dedicated $\beta^*=90$ m LHC optics. Pion pairs were detected by the ATLAS Inner Detector whereas the outgoing protons were measured by ALFA (Absolute Luminosity For ATLAS) detector situated on both sides of ATLAS forward region $\sim$240 m from the ATLAS Interaction Point (IP). An overview of the analysis results is presented as well as a comparison of obtained measurements with relevant model predictions.