| Series |
context_tracking,x86: Defer some IPIs until a user->kernel transition
|
expand
-
[RFC,v3,00/15] context_tracking,x86: Defer some IPIs until a user->kernel transition
-
[RFC,v3,01/15] objtool: Make validate_call() recognize indirect calls to pv_ops[]
-
[RFC,v3,02/15] objtool: Flesh out warning related to pv_ops[] calls
-
[RFC,v3,03/15] sched/clock: Make sched_clock_running __ro_after_init
-
[RFC,v3,04/15] rcu: Add a small-width RCU watching counter debug option
-
[RFC,v3,05/15] rcutorture: Make TREE04 use CONFIG_RCU_DYNTICKS_TORTURE
-
[RFC,v3,06/15] jump_label: Add forceful jump label type
-
[RFC,v3,07/15] x86/speculation/mds: Make mds_idle_clear forceful
-
[RFC,v3,08/15] sched/clock, x86: Make __sched_clock_stable forceful
-
[RFC,v3,09/15] objtool: Warn about non __ro_after_init static key usage in .noinstr
-
[RFC,v3,10/15] x86/alternatives: Record text_poke's of JUMP_TYPE_FORCEFUL labels
-
[RFC,v3,11/15] context-tracking: Introduce work deferral infrastructure
-
[RFC,v3,12/15] context_tracking,x86: Defer kernel text patching IPIs
-
[RFC,v3,13/15] context_tracking,x86: Add infrastructure to defer kernel TLBI
-
[RFC,v3,14/15] x86/mm, mm/vmalloc: Defer flush_tlb_kernel_range() targeting NOHZ_FULL CPUs
-
[RFC,v3,15/15] context-tracking: Add a Kconfig to enable IPI deferral for NO_HZ_IDLE
|
Context ======= We've observed within Red Hat that isolated, NOHZ_FULL CPUs running a pure-userspace application get regularly interrupted by IPIs sent from housekeeping CPUs. Those IPIs are caused by activity on the housekeeping CPUs leading to various on_each_cpu() calls, e.g.: 64359.052209596 NetworkManager 0 1405 smp_call_function_many_cond (cpu=0, func=do_kernel_range_flush) smp_call_function_many_cond+0x1 smp_call_function+0x39 on_each_cpu+0x2a flush_tlb_kernel_range+0x7b __purge_vmap_area_lazy+0x70 _vm_unmap_aliases.part.42+0xdf change_page_attr_set_clr+0x16a set_memory_ro+0x26 bpf_int_jit_compile+0x2f9 bpf_prog_select_runtime+0xc6 bpf_prepare_filter+0x523 sk_attach_filter+0x13 sock_setsockopt+0x92c __sys_setsockopt+0x16a __x64_sys_setsockopt+0x20 do_syscall_64+0x87 entry_SYSCALL_64_after_hwframe+0x65 The heart of this series is the thought that while we cannot remove NOHZ_FULL CPUs from the list of CPUs targeted by these IPIs, they may not have to execute the callbacks immediately. Anything that only affects kernelspace can wait until the next user->kernel transition, providing it can be executed "early enough" in the entry code. The original implementation is from Peter [1]. Nicolas then added kernel TLB invalidation deferral to that [2], and I picked it up from there. Deferral approach ================= Storing each and every callback, like a secondary call_single_queue turned out to be a no-go: the whole point of deferral is to keep NOHZ_FULL CPUs in userspace for as long as possible - no signal of any form would be sent when deferring an IPI. This means that any form of queuing for deferred callbacks would end up as a convoluted memory leak. Deferred IPIs must thus be coalesced, which this series achieves by assigning IPIs a "type" and having a mapping of IPI type to callback, leveraged upon kernel entry. What about IPIs whose callback take a parameter, you may ask? Peter suggested during OSPM23 [3] that since on_each_cpu() targets housekeeping CPUs *and* isolated CPUs, isolated CPUs can access either global or housekeeping-CPU-local state to "reconstruct" the data that would have been sent via the IPI. This series does not affect any IPI callback that requires an argument, but the approach would remain the same (one coalescable callback executed on kernel entry). Kernel entry vs execution of the deferred operation =================================================== This is what I've referred to as the "Danger Zone" during my LPC24 talk [4]. There is a non-zero length of code that is executed upon kernel entry before the deferred operation can be itself executed (i.e. before we start getting into context_tracking.c proper), i.e.: idtentry_func_foo() <--- we're in the kernel irqentry_enter() enter_from_user_mode() __ct_user_exit() ct_kernel_enter_state() ct_work_flush() <--- deferred operation is executed here This means one must take extra care to what can happen in the early entry code, and that <bad things> cannot happen. For instance, we really don't want to hit instructions that have been modified by a remote text_poke() while we're on our way to execute a deferred sync_core(). Patches doing the actual deferral have more detail on this. Patches ======= o Patches 1-3 are standalone cleanups. o Patches 4-5 add an RCU testing feature. o Patches 6-8 add a new type of jump label for static keys that will not have their IPI be deferred. o Patch 9 adds objtool verification of static keys vs their text_poke IPI deferral o Patches 10-14 add the actual IPI deferrals o Patch 15 is a freebie to enable the deferral feature for NO_HZ_IDLE Patches are also available at: https://gitlab.com/vschneid/linux.git -b redhat/isolirq/defer/v3 RFC status ========== Things I'd like to get comments on and/or that are a bit WIPish; they're called out in the individual changelogs: o "forceful" jump label naming which I don't particularly like o objtool usage of 'offset_of(static_key.type)' and JUMP_TYPE_FORCEFUL. I've hardcoded them but it could do with being shoved in a kernel header objtool can include directly o The noinstr variant of __flush_tlb_all() doesn't have a paravirt variant, does it need one? Testing ======= Xeon E5-2699 system with SMToff, NOHZ_FULL, isolated CPUs. RHEL9 userspace. Workload is using rteval (kernel compilation + hackbench) on housekeeping CPUs and a dummy stay-in-userspace loop on the isolated CPUs. The main invocation is: $ trace-cmd record -e "csd_queue_cpu" -f "cpu & CPUS{$ISOL_CPUS}" \ -e "ipi_send_cpumask" -f "cpumask & CPUS{$ISOL_CPUS}" \ -e "ipi_send_cpu" -f "cpu & CPUS{$ISOL_CPUS}" \ rteval --onlyload --loads-cpulist=$HK_CPUS \ --hackbench-runlowmem=True --duration=$DURATION This only records IPIs sent to isolated CPUs, so any event there is interference (with a bit of fuzz at the start/end of the workload when spawning the processes). All tests were done with a duration of 1hr. v6.12-rc4 # This is the actual IPI count $ trace-cmd report trace-base.dat | grep callback | awk '{ print $(NF) }' | sort | uniq -c | sort -nr 1782 callback=generic_smp_call_function_single_interrupt+0x0 73 callback=0x0 # These are the different CSD's that caused IPIs $ trace-cmd report | grep csd_queue | awk '{ print $(NF-1) }' | sort | uniq -c | sort -nr 22048 func=tlb_remove_table_smp_sync 16536 func=do_sync_core 2262 func=do_flush_tlb_all 182 func=do_kernel_range_flush 144 func=rcu_exp_handler 60 func=sched_ttwu_pending v6.12-rc4 + patches: # This is the actual IPI count $ trace-cmd report | grep callback | awk '{ print $(NF) }' | sort | uniq -c | sort -nr 1168 callback=generic_smp_call_function_single_interrupt+0x0 74 callback=0x0 # These are the different CSD's that caused IPIs $ trace-cmd report | grep csd_queue | awk '{ print $(NF-1) }' | sort | uniq -c | sort -nr 23686 func=tlb_remove_table_smp_sync 192 func=rcu_exp_handler 65 func=sched_ttwu_pending Interestingly tlb_remove_table_smp_sync() started showing up on this machine, while it didn't during testing for v2 and it's the same machine. Yair had a series adressing this [5] which per these results would be worth revisiting. Acknowledgements ================ Special thanks to: o Clark Williams for listening to my ramblings about this and throwing ideas my way o Josh Poimboeuf for his guidance regarding objtool and hinting at the .data..ro_after_init section. o All of the folks who attended various talks about this and provided precious feedback. Links ===== [1]: https://lore.kernel.org/all/20210929151723.162004989@infradead.org/ [2]: https://github.com/vianpl/linux.git -b ct-work-defer-wip [3]: https://youtu.be/0vjE6fjoVVE [4]: https://lpc.events/event/18/contributions/1889/ [5]: https://lore.kernel.org/lkml/20230620144618.125703-1-ypodemsk@redhat.com/ Revisions ========= RFCv2 -> RFCv3 +++++++++++ o Rebased onto v6.12-rc7 o Added objtool documentation for the new warning (Josh) o Added low-size RCU watching counter to TREE04 torture scenario (Paul) o Added FORCEFUL jump label and static key types o Added noinstr-compliant helpers for tlb flush deferral o Overall changelog & comments cleanup RFCv1 -> RFCv2 ++++++++++++++ o Rebased onto v6.5-rc1 o Updated the trace filter patches (Steven) o Fixed __ro_after_init keys used in modules (Peter) o Dropped the extra context_tracking atomic, squashed the new bits in the existing .state field (Peter, Frederic) o Added an RCU_EXPERT config for the RCU dynticks counter size, and added an rcutorture case for a low-size counter (Paul) o Fixed flush_tlb_kernel_range_deferrable() definition Valentin Schneider (15): objtool: Make validate_call() recognize indirect calls to pv_ops[] objtool: Flesh out warning related to pv_ops[] calls sched/clock: Make sched_clock_running __ro_after_init rcu: Add a small-width RCU watching counter debug option rcutorture: Make TREE04 use CONFIG_RCU_DYNTICKS_TORTURE jump_label: Add forceful jump label type x86/speculation/mds: Make mds_idle_clear forceful sched/clock, x86: Make __sched_clock_stable forceful objtool: Warn about non __ro_after_init static key usage in .noinstr x86/alternatives: Record text_poke's of JUMP_TYPE_FORCEFUL labels context-tracking: Introduce work deferral infrastructure context_tracking,x86: Defer kernel text patching IPIs context_tracking,x86: Add infrastructure to defer kernel TLBI x86/mm, mm/vmalloc: Defer flush_tlb_kernel_range() targeting NOHZ_FULL CPUs context-tracking: Add a Kconfig to enable IPI deferral for NO_HZ_IDLE arch/Kconfig | 9 +++ arch/x86/Kconfig | 1 + arch/x86/include/asm/context_tracking_work.h | 20 +++++++ arch/x86/include/asm/special_insns.h | 1 + arch/x86/include/asm/text-patching.h | 13 ++++- arch/x86/include/asm/tlbflush.h | 17 +++++- arch/x86/kernel/alternative.c | 49 ++++++++++++---- arch/x86/kernel/cpu/bugs.c | 2 +- arch/x86/kernel/cpu/common.c | 6 +- arch/x86/kernel/jump_label.c | 7 ++- arch/x86/kernel/kprobes/core.c | 4 +- arch/x86/kernel/kprobes/opt.c | 4 +- arch/x86/kernel/module.c | 2 +- arch/x86/mm/tlb.c | 49 ++++++++++++++-- include/linux/context_tracking.h | 21 +++++++ include/linux/context_tracking_state.h | 54 ++++++++++++++--- include/linux/context_tracking_work.h | 28 +++++++++ include/linux/jump_label.h | 26 ++++++--- kernel/context_tracking.c | 46 ++++++++++++++- kernel/rcu/Kconfig.debug | 14 +++++ kernel/sched/clock.c | 4 +- kernel/time/Kconfig | 19 ++++++ mm/vmalloc.c | 35 +++++++++-- tools/objtool/Documentation/objtool.txt | 13 +++++ tools/objtool/check.c | 58 ++++++++++++++++--- tools/objtool/include/objtool/check.h | 1 + tools/objtool/include/objtool/special.h | 2 + tools/objtool/special.c | 3 + .../selftests/rcutorture/configs/rcu/TREE04 | 1 + 29 files changed, 450 insertions(+), 59 deletions(-) create mode 100644 arch/x86/include/asm/context_tracking_work.h create mode 100644 include/linux/context_tracking_work.h -- 2.43.0