On 31/01/2024 15:05, David Hildenbrand wrote: > On 31.01.24 16:02, Ryan Roberts wrote: >> On 31/01/2024 14:29, David Hildenbrand wrote: >>>>> Note that regarding NUMA effects, I mean when some memory access within the >>>>> same >>>>> socket is faster/slower even with only a single node. On AMD EPYC that's >>>>> possible, depending on which core you are running and on which memory >>>>> controller >>>>> the memory you want to access is located. If both are in different quadrants >>>>> IIUC, the access latency will be different. >>>> >>>> I've configured the NUMA to only bring the RAM and CPUs for a single socket >>>> online, so I shouldn't be seeing any of these effects. Anyway, I've been using >>>> the Altra as a secondary because its so much slower than the M2. Let me move >>>> over to it and see if everything looks more straightforward there. >>> >>> Better use a system where people will actually run Linux production workloads >>> on, even if it is slower :) >>> >>> [...] >>> >>>>>> >>>>>> I'll continue to mess around with it until the end of the day. But I'm not >>>>>> making any headway, then I'll change tack; I'll just measure the >>>>>> performance of >>>>>> my contpte changes using your fork/zap stuff as the baseline and post >>>>>> based on >>>>>> that. >>>>> >>>>> You should likely not focus on M2 results. Just pick a representative bare >>>>> metal >>>>> machine where you get consistent, explainable results. >>>>> >>>>> Nothing in the code is fine-tuned for a particular architecture so far, only >>>>> order-0 handling is kept separate. >>>>> >>>>> BTW: I see the exact same speedups for dontneed that I see for munmap. For >>>>> example, for order-9, it goes from 0.023412s -> 0.009785, so -58%. So I'm >>>>> curious why you see a speedup for munmap but not for dontneed. >>>> >>>> Ugh... ok, coming up. >>> >>> Hopefully you were just staring at the wrong numbers (e.g., only with fork >>> patches). Because both (munmap/pte-dontneed) are using the exact same code path. >>> >> >> Ahh... I'm doing pte-dontneed, which is the only option in your original >> benchmark - it does MADV_DONTNEED one page at a time. It looks like your new >> benchmark has an additional "dontneed" option that does it in one shot. Which >> option are you running? Assuming the latter, I think that explains it. > > I temporarily removed that option and then re-added it. Guess you got a wrong > snapshot of the benchmark :D > > pte-dontneed not observing any change is great (no batching possible). indeed. > > dontneed should hopefully/likely see a speedup. Yes, but that's almost exactly the same path as munmap, so I'm sure it really adds much for this particular series. Anyway, on Altra at least, I'm seeing no regressions, so: Tested-by: Ryan Roberts <ryan.roberts@xxxxxxx> > > Great! >
