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But instead of using restartable sequences as API to set the flag >>>>>>> to request the extension, this patch proposes a new API with use of a per >>>>>>> thread shared structure implementation described below. This shared structure >>>>>>> is accessible in both users pace and kernel. The user thread will set the >>>>>>> flag in this shared structure to request execution time extension. >>>>>> But why -- we already have rseq, glibc uses it by default. Why add yet >>>>>> another thing? >>>>> >>>>> Indeed, what I'm not seeing in this RFC patch series cover letter is an >>>>> explanation that justifies adding yet another per-thread memory area >>>>> shared between kernel and userspace when we have extensible rseq >>>>> already. >>>> >>>> It mainly provides pinned memory, can be useful for future use cases >>>> where updating user memory in kernel context can be fast or needs to >>>> avoid pagefaults. >>> >>> 'might be useful' it not good enough a justification. Also, I don't >>> think you actually need this. >> >> Will get back with database benchmark results using rseq API for scheduler time extension. > > Sorry about the delay in response. > > Here are the database swingbench numbers - includes results with use of rseq API. > > Test results: > ========= > Test system 2 socket AMD Genoa > > Swingbench - standard database benchmark > Cached(database files on tmpfs) run, with 1000 clients. > > Baseline(Without Sched time extension): 99K SQL exec/sec > > With Sched time extension: > Shared structure API use: 153K SQL exec/sec (Previously reported) > 55% improvement in throughput. > > Restartable sequences API use: 147K SQL exec/sec > 48% improvement in throughput > > While both show good performance benefit with scheduler time extension, > there is a 7% difference in throughput between Shared structure & Restartable sequences API. > Use of shared structure is faster. Can you share the code for both test cases ? And do you have relevant perf profile showing where time is spent ? Thanks, Mathieu > > > >> >>> >>> See: >>> >>> https://lkml.kernel.org/r/20220113233940.3608440-4-posk@google.com >>> >>> for a more elaborate scheme. >>> >>>>> Peter, was there anything fundamentally wrong with your approach based >>>>> on rseq ? https://lore.kernel.org/lkml/20231030132949.GA38123@noisy.programming.kicks-ass.net >>>>> >>>>> The main thing I wonder is whether loading the rseq delay resched flag >>>>> on return to userspace is too late in your patch. Also, I'm not sure it is >>>>> realistic to require that no system calls should be done within time extension >>>>> slice. If we have this scenario: >>>> >>>> I am also not sure if we need to prevent system calls in this scenario. >>>> Was that restriction mainly because of restartable sequence API implements it? >>> >>> No, the whole premise of delaying resched was because people think that >>> syscalls are too slow. If you do not think this, then you shouldn't be >>> using this. >> >> Agree. >> >> Thanks, >> -Prakash > > -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com