A log file sync wait event is commonly attributed to either a lack of IO or CPU resources, or both. If the bottleneck is both CPU and IO, it tends to quickly shift between the two, which when averaged over an interval, does not clearly show either one to be a problem. This can easily cloud your understanding of the situation, so you must be very careful.

Remain focused on the application commit times. If the log writer is pushing more IO (requirements) than the IO subsystem can absorb (capacity), the top wait event will be log file parallel write, with average wait times greater than 10 ms and high IO subsystem response times gathered from iostat or sar. If the IO subsystem is responding poorly, the server process posting the log file sync will indeed need to wait for the log writer background process to finish writing.

There is more to committing a transaction than simply triggering the log writer to write. Commits involve overhead in preparing for the write, updating Oracle internal structures (requiring latches and memory manipulation), and actually issuing the write. Rapid commits also lower the log writer's efficiency, as each write will not be as packed full of redo. So while the IO subsystem may be suffering, the log file sync points more toward an application issue rather than an IO subsystem issue. But this is no excuse for the IO subsystem team to abdicate their responsibility of ensuring the IO subsystem can process Oracle's IO requirements.