On 1/23/2025 9:53 AM, Rik van Riel wrote: > Add support for broadcast TLB invalidation using AMD's INVLPGB instruction. > > This allows the kernel to invalidate TLB entries on remote CPUs without > needing to send IPIs, without having to wait for remote CPUs to handle > those interrupts, and with less interruption to what was running on > those CPUs. > > Because x86 PCID space is limited, and there are some very large > systems out there, broadcast TLB invalidation is only used for > processes that are active on 3 or more CPUs, with the threshold > being gradually increased the more the PCID space gets exhausted. > > Combined with the removal of unnecessary lru_add_drain calls > (see https://lkml.org/lkml/2024/12/19/1388) this results in a > nice performance boost for the will-it-scale tlb_flush2_threads > test on an AMD Milan system with 36 cores: > > - vanilla kernel: 527k loops/second > - lru_add_drain removal: 731k loops/second > - only INVLPGB: 527k loops/second > - lru_add_drain + INVLPGB: 1157k loops/second > > Profiling with only the INVLPGB changes showed while > TLB invalidation went down from 40% of the total CPU > time to only around 4% of CPU time, the contention > simply moved to the LRU lock. > > Fixing both at the same time about doubles the > number of iterations per second from this case. > > Some numbers closer to real world performance > can be found at Phoronix, thanks to Michael: > > https://www.phoronix.com/news/AMD-INVLPGB-Linux-Benefits > > My current plan is to implement support for Intel's RAR > (Remote Action Request) TLB flushing in a follow-up series, > after this thing has been merged into -tip. Making things > any larger would just be unwieldy for reviewers. > > v7: > - a few small code cleanups (Nadav) > - fix spurious VM_WARN_ON_ONCE in mm_global_asid > - code simplifications & better barriers (Peter & Dave) > v6: > - fix info->end check in flush_tlb_kernel_range (Michael) > - disable broadcast TLB flushing on 32 bit x86 > v5: > - use byte assembly for compatibility with older toolchains (Borislav, Michael) > - ensure a panic on an invalid number of extra pages (Dave, Tom) > - add cant_migrate() assertion to tlbsync (Jann) > - a bunch more cleanups (Nadav) > - key TCE enabling off X86_FEATURE_TCE (Andrew) > - fix a race between reclaim and ASID transition (Jann) > v4: > - Use only bitmaps to track free global ASIDs (Nadav) > - Improved AMD initialization (Borislav & Tom) > - Various naming and documentation improvements (Peter, Nadav, Tom, Dave) > - Fixes for subtle race conditions (Jann) > v3: > - Remove paravirt tlb_remove_table call (thank you Qi Zheng) > - More suggested cleanups and changelog fixes by Peter and Nadav > v2: > - Apply suggestions by Peter and Borislav (thank you!) > - Fix bug in arch_tlbbatch_flush, where we need to do both > the TLBSYNC, and flush the CPUs that are in the cpumask. > - Some updates to comments and changelogs based on questions. > > I have collected performance data using the will-it-scale tlb_flush2_threads benchmark on my AMD Milan, Genoa, and Turin systems. As expected, I don't see any discrepancies in the data. (Performance Testing is done based on 6.13.0-rc7). ------------------------------------------------------------------------------------------------------------------------------------------------ | ./tlb_flush2_threads -s 5 -t 128 | Milan 1P (NPS1) | Milan 1P (NPS2) | Genoa 1P (NPS1) | Genoa 1P (NPS2) | Turin 2P (NPS1) | Turin 2P (NPS2) | ------------------------------------------------------------------------------------------------------------------------------------------------ | Vanila | 357647 | 419631 | 319885 | 311069 | 380559 | 379286 | ------------------------------------------------------------------------------------------------------------------------------------------------ | LRU drain removal | 784734 | 796056 | 540862 | 530472 | 549168 | 482683 | ------------------------------------------------------------------------------------------------------------------------------------------------ | INVLPGB | 581069 | 950848 | 501033 | 553987 | 528660 | 536535 | ------------------------------------------------------------------------------------------------------------------------------------------------ | LRU drain removal + INVLPGB | 1094941 | 1086826 | 980293 | 979005 | 1228823 | 1238440 | ------------------------------------------------------------------------------------------------------------------------------------------------ | LRU drain vs. Vanila | 54.42% | 47.29% | 40.86% | 41.36% | 30.70% | 21.42% | ------------------------------------------------------------------------------------------------------------------------------------------------ | INVLPGB vs. Vanila | 38.45% | 55.87% | 55.87% | 43.85% | 28.01% | 29.31% | ------------------------------------------------------------------------------------------------------------------------------------------------ | (LRU drain + INVLPGB) vs. Vanila | 67.34% | 61.39% | 67.37% | 68.23% | 69.03% | 69.37% | ------------------------------------------------------------------------------------------------------------------------------------------------ Feel free to add: Tested-by: Manali Shukla <Manali.Shukla@xxxxxxx> I would be happy to test future versions, if needed. -Manali
