Message-ID: <5861243.DvuYhMxLoT@natalenko.name>
Date: Sat, 22 Feb 2025 12:29:54 +0100
From: Oleksandr Natalenko <oleksandr@...alenko.name>
To: x86@...nel.org, Rik van Riel <riel@...riel.com>
Cc: linux-kernel@...r.kernel.org, bp@...en8.de, peterz@...radead.org,
 dave.hansen@...ux.intel.com, zhengqi.arch@...edance.com,
 nadav.amit@...il.com, thomas.lendacky@....com, kernel-team@...a.com,
 linux-mm@...ck.org, akpm@...ux-foundation.org, jackmanb@...gle.com,
 jannh@...gle.com, mhklinux@...look.com, andrew.cooper3@...rix.com,
 Manali.Shukla@....com
Subject: Re: [PATCH v12 00/16] AMD broadcast TLB invalidation

Hello.

On pátek 21. února 2025 1:52:59, středoevropský standardní čas 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.
> 
> v12:
>  - make sure "nopcid" command line option turns off invlpgb (Brendan)
>  - add "noinvlpgb" kernel command line option
>  - split out kernel TLB flushing differently (Dave & Yosry)
>  - split up the patch that does invlpgb flushing for user processes (Dave)
>  - clean up get_flush_tlb_info (Boris)
>  - move invlpgb_count_max initialization to get_cpu_cap (Boris)
>  - bunch more comments as requested

Somehow, this iteration breaks resume from S3. I can see it even in a QEMU VM:

```
[   24.373391] ACPI: PM: Low-level resume complete
[   24.373929] ACPI: PM: Restoring platform NVS memory
[   24.375024] Enabling non-boot CPUs ...
[   24.375777] smpboot: Booting Node 0 Processor 1 APIC 0x1
[   24.376463] BUG: unable to handle page fault for address: ffffffffa3ba4d60
[   24.377383] #PF: supervisor write access in kernel mode
[   24.377912] #PF: error_code(0x0003) - permissions violation
[   24.378413] PGD 25427067 P4D 25427067 PUD 25428063 PMD 8000000024c001a1
[   24.379020] Oops: Oops: 0003 [#1] PREEMPT SMP NOPTI
[   24.379503] CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Kdump: loaded Not tainted 6.14.0-pf0 #1 161e4891fb5044b2d7438cd1852eeaac0cdffab5
[   24.380650] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS unknown 02/02/2022
[   24.381400] RIP: 0010:get_cpu_cap+0x39b/0x4f0
[   24.381810] Code: 08 c7 44 24 08 00 00 00 00 48 8d 4c 24 0c e8 3c 00 04 00 90 8b 44 24 04 89 43 64 0f b7 44 24 0c 83 c0 01 81 7b 24 09 00 00 80 <66> 89 05 0e ab 8b 01 0f 86 18 fd ff ff c7 44 24 14 00 00 00 00 4c
[   24.383629] RSP: 0000:ffffafbec00efe70 EFLAGS: 00010012
[   24.384155] RAX: 0000000000000001 RBX: ffff8b3fbcb19020 RCX: 0000000000001001
[   24.384862] RDX: 0000000000000000 RSI: ffffafbec00efe74 RDI: ffffafbec00efe78
[   24.385603] RBP: ffffafbec00efe88 R08: ffffafbec00efe70 R09: ffffafbec00efe7c
[   24.386318] R10: 0000000000002430 R11: ffff8b3fa5428000 R12: ffffafbec00efe8c
[   24.387014] R13: ffffafbec00efe84 R14: ffffafbec00efe80 R15: ffffafbec00efe70
[   24.387713] FS:  0000000000000000(0000) GS:ffff8b3fbcb00000(0000) knlGS:0000000000000000
[   24.388502] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   24.389074] CR2: ffffffffa3ba4d60 CR3: 0000000025422000 CR4: 0000000000350ef0
[   24.389769] Call Trace:
[   24.390020]  <TASK>
[   24.392234]  identify_cpu+0xd4/0x890
[   24.392593]  identify_secondary_cpu+0x12/0x40
[   24.393032]  smp_store_cpu_info+0x49/0x60
[   24.393430]  start_secondary+0x7f/0x140
[   24.393810]  common_startup_64+0x13e/0x141
[   24.394218]  </TASK>

$ scripts/faddr2line arch/x86/kernel/cpu/common.o get_cpu_cap+0x39b
get_cpu_cap+0x39b/0x500:
get_cpu_cap at …/arch/x86/kernel/cpu/common.c:1063

1060         if (c->extended_cpuid_level >= 0x80000008) {
1061                 cpuid(0x80000008, &eax, &ebx, &ecx, &edx);
1062                 c->x86_capability[CPUID_8000_0008_EBX] = ebx;
1063                 invlpgb_count_max = (edx & 0xffff) + 1;
1064         }
```

Any idea what I'm looking at?

Thank you.

> v11:
>  - resolve conflict with CONFIG_PT_RECLAIM code
>  - a few more cleanups (Peter, Brendan, Nadav)
> v10:
>  - simplify partial pages with min(nr, 1) in the invlpgb loop (Peter)
>  - document x86 paravirt, AMD invlpgb, and ARM64 flush without IPI (Brendan)
>  - remove IS_ENABLED(CONFIG_X86_BROADCAST_TLB_FLUSH) (Brendan)
>  - various cleanups (Brendan)
> v9:
>  - print warning when start or end address was rounded (Peter)
>  - in the reclaim code, tlbsync at context switch time (Peter)
>  - fix !CONFIG_CPU_SUP_AMD compile error in arch_tlbbatch_add_pending (Jan)
> v8:
>  - round start & end to handle non-page-aligned callers (Steven & Jan)
>  - fix up changelog & add tested-by tags (Manali)
> 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.
> 
> 
> 


-- 
Oleksandr Natalenko, MSE
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