Back in 2012, Microsoft released the 64-bit exFAT (Extended File Allocation Table) file system as the successor to the 32-bit FAT32. Seven years later in 2019, the Redmond giant made a big revelation when it announced exFAT format support on Linux. Fast forward three years to now and it looks like exFAT is about to get a heavy performance boost in the upcoming Linux 6.2, thanks to Sony’s latest effort. Yuezhang Mo, an engineer for the Japanese tech giant, found that the reduction was repeating itself Transition of library values Greatly improves the performance of exFAT. And this is especially noticeable in the case of lower end processors.

Mo explains his own Fix:

After traversing all directory entries, hint at the empty directory entry, regardless of whether there are enough empty directory entries or not.

After this commit, hint the empty library entries like this:

1. Hint the deleted library entries if enough;

2. Hint the deleted and unused library entries at the end of the cluster chain regardless of whether there are enough or not (add according to this commitment);

3. If there are no empty directory entries, hint the empty directory entries in the new cluster (add per this commit).

This prevents re-passing of directory entries, reduces CPU usage, and improves the performance of file and directory creation (especially on low-performance CPUs).

In order to reach this conclusion, tests were performed using 5000 files. The interesting thing noted was that the improvement increased with the number of file sizes. The biggest gain seen was almost 58%. The test was conducted on a SABER i.MX6 Lite development board using a Class 4 SD card:

	before	to another	improvement
1~1000	25.360 seconds	22.168 seconds	14.40%
1001~2000	38.242 seconds	28.72ss [sic]	33.15%
2001~3000	49.134 seconds	35.037 seconds	40.23%
3001~4000	62.042 seconds	41.624 seconds	49.05%
4001~5000	73.629 seconds	46.772 seconds	57.42%

Interestingly, this isn’t the first time Sony has pushed fixes to exFAT that made massive performance improvements. Back in April, Yuezhang Mo pointed this out with DirSync is enabledThere was an improvement of up to 85.4% in some cases.

Through: Furonics