On 8/10/21 6:04 PM, Jens Axboe wrote: > On 8/10/21 7:52 AM, Pavel Begunkov wrote: >> For requests with non-fixed files, instead of grabbing just one >> reference, we get by the number of left requests, so the following >> requests using the same file can take it without atomics. >> >> However, it's not all win. If there is one request in the middle >> not using files or having a fixed file, we'll need to put back the left >> references. Even worse if an application submits requests dealing with >> different files, it will do a put for each new request, so doubling the >> number of atomics needed. Also, even if not used, it's still takes some >> cycles in the submission path. >> >> If a file used many times, it rather makes sense to pre-register it, if >> not, we may fall in the described pitfall. So, this optimisation is a >> matter of use case. Go with the simpliest code-wise way, remove it. > > I ran this through the peak testing, not using registered files. Doesn't > seem to make a real difference here, at least in the quick testing. > Which would seem to indicate we could safely kill it. But that's also > the best case for non-registered files, would be curious to see if it > makes a real difference now for workloads where the file is being > shared. Do you mean shared between cores so there is contention? Or the worst case for non-reg with multiple files as described in the patch? -- Pavel Begunkov
