On Mon, Dec 05, 2022 at 02:55:48PM +0000, Luther, Sven wrote: > #regzbot ^introduced 10befea91b61c4e2c2d1df06a2e978d182fcf792 > > We are making heavy use of mqueues, and noticed a degradation of performance between 4.18 & 5.10 linux kernels. > > After a gross per-version tracing, we did kernel bisection between 5.8 and 5.9 > and traced the issue to a 10 patches (of which 9 where skipped as they didn't boot) between: > > > commit 10befea91b61c4e2c2d1df06a2e978d182fcf792 (HEAD, refs/bisect/bad) > Author: Roman Gushchin <guro@xxxxxx> > Date: Thu Aug 6 23:21:27 2020 -0700 > > mm: memcg/slab: use a single set of kmem_caches for all allocations > > and: > > commit 286e04b8ed7a04279ae277f0f024430246ea5eec (refs/bisect/good-286e04b8ed7a04279ae277f0f024430246ea5eec) > Author: Roman Gushchin <guro@xxxxxx> > Date: Thu Aug 6 23:20:52 2020 -0700 > > mm: memcg/slab: allocate obj_cgroups for non-root slab pages > > All of them are part of the "The new cgroup slab memory controller" patchset: > > https://lore.kernel.org/all/20200623174037.3951353-18-guro@xxxxxx/T/ > > from Roman Gushchin, which moves the accounting for page level to the object level. > > Measurements where done using the a test programmtest, which measures mix/average/max time mqueue_send/mqueue_rcv, > and average for getppid, both measured over 100 000 runs. Results are shown in the following table > > +----------+--------------------------+-------------------------+----------------+ > | kernel | mqueue_rcv (ns) | mqueue_send (ns) | getppid | > | version | min avg max variation | min avg max variation | (ns) variation | > +----------+--------------------------+-------------------------+----------------+ > | 4.18.45 | 351 382 17533 base | 383 410 13178 base | 149 base | > | 5.8-good | 380 392 7156 -2,55% | 376 384 6225 6,77% | 169 -11,83% | > | 5.8-bad | 524 530 5310 -27,92% | 512 519 8775 -21,00% | 169 -11,83% | > | 5.10 | 520 533 4078 -28,33% | 518 534 8108 -23,22% | 167 -10,78% | > | 5.15 | 431 444 8440 -13,96% | 425 437 6170 -6,18% | 171 -12,87% | > | 6.03 | 474 614 3881 -37,79% | 482 693 931 -40,84% | 171 -12,87% | > +----------+--------------------------+-------------------------+----------------- Hi Sven! Thank you for the report! As Waiman said, it's not a secret that per-object tracking makes individual allocations slower, but for the majority of workloads it's well compensated by significant memory savings and a lower fragmentation. It seems there is another regression between 5.15 and 6.03, which is a separate topic, but how big is the real regression between 4.18 and 5.15? The benchmark shows about 14%, but is you real workload suffering at the same level? If the answer is yes, the right thing to do is to introduce some sort of mqueue-specific caching for allocated objects. Thanks! Roman
