There are several sources of timing information, and I think in this context "nanosecond precision" just means that Tracy is able to accurately represent and handle input in nanoseconds.
The resolution of the actual measurements depends on the kind of measurement:
1. If the measurement is based on high resolution timers on the CPU, the resolution depends on the hardware and the OS. On Windows, `QueryPerformanceFrequency()` returns the resolution, and I believe it is often in the order of 10s or 100s of nanoseconds.
2. If the measurement is based on GPU-side performance counters, it depends on the driver and the hardware. Graphics APIs allow you to query the "time-per-tick" value to translate from performance counters to nanoseconds. Performance counters can be down to "number of instructions executed", and since a single instruction can be on the order of 1-2 nanoseconds in some cases, translating a performance counter value to a time period requires nanosecond precision.
3. Modern GPUs also include their own high-precision timers for profiling things that are not necessarily easy to capture with performance counters (like barriers, contention, and complicated cache interactions).
Yes, that's my understanding and why I asked. I disagree about "in this context", though, which is a pitch. If I was going to buy hardware that claimed ns resolution for something I was building I would expect 1ns resolution, not "something around a few ns" and not qualified "only on particular hardware". If such a product were presenting itself in a straightforward way to be compared to similar products and respecting the potential user it would say "resolutions down to a few ns" or something more specific but accurate.
There was even a discussion on this not long ago on how to market to technical folks and things to not do (this is one of the things not to do)
The resolution of the actual measurements depends on the kind of measurement:
1. If the measurement is based on high resolution timers on the CPU, the resolution depends on the hardware and the OS. On Windows, `QueryPerformanceFrequency()` returns the resolution, and I believe it is often in the order of 10s or 100s of nanoseconds.
2. If the measurement is based on GPU-side performance counters, it depends on the driver and the hardware. Graphics APIs allow you to query the "time-per-tick" value to translate from performance counters to nanoseconds. Performance counters can be down to "number of instructions executed", and since a single instruction can be on the order of 1-2 nanoseconds in some cases, translating a performance counter value to a time period requires nanosecond precision.
3. Modern GPUs also include their own high-precision timers for profiling things that are not necessarily easy to capture with performance counters (like barriers, contention, and complicated cache interactions).