On Mon, 3 Jun 2024, Shravan Ramani wrote: > > > Both these features are supported by BlueField-3 PMC hardware, hence > > > the required bit-fields are exposed by the driver via sysfs to allow > > > the user to configure as needed. > > > > I'm trying to understand what happens for the other counter, when the > > use_odd_counter is enabled? This change also doesn't add code that would > > make the other counter -EBUSY, should that be done? > > When 2 32-bit counters are coupled to form a 64-bit counter using this setting, > one counter will hold the lower 32 bits while the other will hold the upper 32. > So the other counter (or syses corresponding to it) also needs to be accessed. > > > For 64-bit counter, I suppose the userspace is expected to read the full > > counter from two sysfs files and combine the value (your documentation > > doesn't explain this)? That seems non-optimal, why cannot kernel just > > return the full combined 64-value directly in kernel? > > I will add more clear comments for this. > While it is true that the driver could combine the 2 fields and present a > 64-bit value via one of the sysfs, the reason for the current approach is that > there are other interfaces which expose the same counters for our platform > and there are tools that are expected to work on top of both interfaces for > the purpose of collecting performance stats. > The other interfaces follow this > approach of having lower and upper 32-bits separately in each counter, and > the tools expect the same. Hence the driver follows this approach to keep > things consistent across the BlueField platform. Hi, I went to look through the existing arrays in mlxbf-pmc.c but did not find any entries that would have clearly indicated the counters being hi/lo parts of the same counter. There were a few 0/1 ones which could be the same counter although I suspect even they are not parts of the same counter but two separate entities called 0 and 1 having the same counter. Could you please elaborate further what you meant with the note about other interfaces above so I can better assess the claim? -- i.
