Message-ID: <e7af023f-39cd-4aa4-aa13-dd6aabea4cdf@arm.com>
Date: Tue, 9 Apr 2024 15:39:29 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: David Hildenbrand <david@...hat.com>,
 Itaru Kitayama <itaru.kitayama@...ux.dev>
Cc: Catalin Marinas <Catalin.Marinas@....com>, Will Deacon <will@...nel.org>,
 Mark Rutland <Mark.Rutland@....com>, Ard Biesheuvel <ardb@...nel.org>,
 Donald Dutile <ddutile@...hat.com>, Eric Chanudet <echanude@...hat.com>,
 Linux ARM <linux-arm-kernel@...ts.infradead.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/4] Speed up boot with faster linear map creation

On 09/04/2024 15:29, David Hildenbrand wrote:
> On 09.04.24 16:13, Ryan Roberts wrote:
>> On 09/04/2024 12:51, David Hildenbrand wrote:
>>> On 09.04.24 13:29, David Hildenbrand wrote:
>>>> On 09.04.24 13:22, David Hildenbrand wrote:
>>>>> On 09.04.24 12:13, Itaru Kitayama wrote:
>>>>>>
>>>>>>
>>>>>>> On Apr 9, 2024, at 19:04, Ryan Roberts <ryan.roberts@....com> wrote:
>>>>>>>
>>>>>>> On 09/04/2024 01:10, Itaru Kitayama wrote:
>>>>>>>> Hi Ryan,
>>>>>>>>
>>>>>>>>> On Apr 8, 2024, at 16:30, Ryan Roberts <ryan.roberts@....com> wrote:
>>>>>>>>>
>>>>>>>>> On 06/04/2024 11:31, Itaru Kitayama wrote:
>>>>>>>>>> Hi Ryan,
>>>>>>>>>>
>>>>>>>>>> On Sat, Apr 06, 2024 at 09:32:34AM +0100, Ryan Roberts wrote:
>>>>>>>>>>> Hi Itaru,
>>>>>>>>>>>
>>>>>>>>>>> On 05/04/2024 08:39, Itaru Kitayama wrote:
>>>>>>>>>>>> On Thu, Apr 04, 2024 at 03:33:04PM +0100, Ryan Roberts wrote:
>>>>>>>>>>>>> Hi All,
>>>>>>>>>>>>>
>>>>>>>>>>>>> It turns out that creating the linear map can take a significant
>>>>>>>>>>>>> proportion of
>>>>>>>>>>>>> the total boot time, especially when rodata=full. And most of the
>>>>>>>>>>>>> time is spent
>>>>>>>>>>>>> waiting on superfluous tlb invalidation and memory barriers. This
>>>>>>>>>>>>> series reworks
>>>>>>>>>>>>> the kernel pgtable generation code to significantly reduce the number
>>>>>>>>>>>>> of those
>>>>>>>>>>>>> TLBIs, ISBs and DSBs. See each patch for details.
>>>>>>>>>>>>>
>>>>>>>>>>>>> The below shows the execution time of map_mem() across a couple of
>>>>>>>>>>>>> different
>>>>>>>>>>>>> systems with different RAM configurations. We measure after applying
>>>>>>>>>>>>> each patch
>>>>>>>>>>>>> and show the improvement relative to base (v6.9-rc2):
>>>>>>>>>>>>>
>>>>>>>>>>>>>                    | Apple M2 VM | Ampere Altra| Ampere Altra| Ampere
>>>>>>>>>>>>> Altra
>>>>>>>>>>>>>                    | VM, 16G     | VM, 64G     | VM, 256G    | Metal,
>>>>>>>>>>>>> 512G
>>>>>>>>>>>>> ---------------|-------------|-------------|-------------|-------------
>>>>>>>>>>>>>                    |   ms    (%) |   ms    (%) |   ms    (%) |
>>>>>>>>>>>>> ms    (%)
>>>>>>>>>>>>> ---------------|-------------|-------------|-------------|-------------
>>>>>>>>>>>>> base           |  153   (0%) | 2227   (0%) | 8798   (0%) | 17442  
>>>>>>>>>>>>> (0%)
>>>>>>>>>>>>> no-cont-remap  |   77 (-49%) |  431 (-81%) | 1727 (-80%) |  3796
>>>>>>>>>>>>> (-78%)
>>>>>>>>>>>>> batch-barriers |   13 (-92%) |  162 (-93%) |  655 (-93%) |  1656
>>>>>>>>>>>>> (-91%)
>>>>>>>>>>>>> no-alloc-remap |   11 (-93%) |  109 (-95%) |  449 (-95%) |  1257
>>>>>>>>>>>>> (-93%)
>>>>>>>>>>>>> lazy-unmap     |    6 (-96%) |   61 (-97%) |  257 (-97%) |   838
>>>>>>>>>>>>> (-95%)
>>>>>>>>>>>>>
>>>>>>>>>>>>> This series applies on top of v6.9-rc2. All mm selftests pass. I've
>>>>>>>>>>>>> compile and
>>>>>>>>>>>>> boot tested various PAGE_SIZE and VA size configs.
>>>>>>>>>>>>>
>>>>>>>>>>>>> ---
>>>>>>>>>>>>>
>>>>>>>>>>>>> Changes since v1 [1]
>>>>>>>>>>>>> ====================
>>>>>>>>>>>>>
>>>>>>>>>>>>>       - Added Tested-by tags (thanks to Eric and Itaru)
>>>>>>>>>>>>>       - Renamed ___set_pte() -> __set_pte_nosync() (per Ard)
>>>>>>>>>>>>>       - Reordered patches (biggest impact & least controversial first)
>>>>>>>>>>>>>       - Reordered alloc/map/unmap functions in mmu.c to aid reader
>>>>>>>>>>>>>       - pte_clear() -> __pte_clear() in clear_fixmap_nosync()
>>>>>>>>>>>>>       - Reverted generic p4d_index() which caused x86 build error.
>>>>>>>>>>>>> Replaced with
>>>>>>>>>>>>>         unconditional p4d_index() define under arm64.
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> [1]
>>>>>>>>>>>>> https://lore.kernel.org/linux-arm-kernel/20240326101448.3453626-1-ryan.roberts@arm.com/<https://lore.kernel.org/linux-arm-kernel/20240326101448.3453626-1-ryan.roberts@arm.com/>
>>>>>>>>>>>>>
>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>> Ryan
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> Ryan Roberts (4):
>>>>>>>>>>>>>       arm64: mm: Don't remap pgtables per-cont(pte|pmd) block
>>>>>>>>>>>>>       arm64: mm: Batch dsb and isb when populating pgtables
>>>>>>>>>>>>>       arm64: mm: Don't remap pgtables for allocate vs populate
>>>>>>>>>>>>>       arm64: mm: Lazily clear pte table mappings from fixmap
>>>>>>>>>>>>>
>>>>>>>>>>>>> arch/arm64/include/asm/fixmap.h  |   5 +-
>>>>>>>>>>>>> arch/arm64/include/asm/mmu.h     |   8 +
>>>>>>>>>>>>> arch/arm64/include/asm/pgtable.h |  13 +-
>>>>>>>>>>>>> arch/arm64/kernel/cpufeature.c   |  10 +-
>>>>>>>>>>>>> arch/arm64/mm/fixmap.c           |  11 +
>>>>>>>>>>>>> arch/arm64/mm/mmu.c              | 377 +++++++++++++++++++++++--------
>>>>>>>>>>>>> 6 files changed, 319 insertions(+), 105 deletions(-)
>>>>>>>>>>>>>
>>>>>>>>>>>>> -- 
>>>>>>>>>>>>> 2.25.1
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> I've build and boot tested the v2 on FVP, base is taken from your
>>>>>>>>>>>> linux-rr repo. Running run_vmtests.sh on v2 left some gup longterm not
>>>>>>>>>>>> oks, would you take a look at it? The mm ksefltests used is from your
>>>>>>>>>>>> linux-rr repo too.
>>>>>>>>>>>
>>>>>>>>>>> Thanks for taking a look at this.
>>>>>>>>>>>
>>>>>>>>>>> I can't reproduce your issue unfortunately; steps as follows on Apple
>>>>>>>>>>> M2 VM:
>>>>>>>>>>>
>>>>>>>>>>> Config: arm64 defconfig + the following:
>>>>>>>>>>>
>>>>>>>>>>> # Squashfs for snaps, xfs for large file folios.
>>>>>>>>>>> ./scripts/config --enable CONFIG_SQUASHFS_LZ4
>>>>>>>>>>> ./scripts/config --enable CONFIG_SQUASHFS_LZO
>>>>>>>>>>> ./scripts/config --enable CONFIG_SQUASHFS_XZ
>>>>>>>>>>> ./scripts/config --enable CONFIG_SQUASHFS_ZSTD
>>>>>>>>>>> ./scripts/config --enable CONFIG_XFS_FS
>>>>>>>>>>>
>>>>>>>>>>> # For general mm debug.
>>>>>>>>>>> ./scripts/config --enable CONFIG_DEBUG_VM
>>>>>>>>>>> ./scripts/config --enable CONFIG_DEBUG_VM_MAPLE_TREE
>>>>>>>>>>> ./scripts/config --enable CONFIG_DEBUG_VM_RB
>>>>>>>>>>> ./scripts/config --enable CONFIG_DEBUG_VM_PGFLAGS
>>>>>>>>>>> ./scripts/config --enable CONFIG_DEBUG_VM_PGTABLE
>>>>>>>>>>> ./scripts/config --enable CONFIG_PAGE_TABLE_CHECK
>>>>>>>>>>>
>>>>>>>>>>> # For mm selftests.
>>>>>>>>>>> ./scripts/config --enable CONFIG_USERFAULTFD
>>>>>>>>>>> ./scripts/config --enable CONFIG_TEST_VMALLOC
>>>>>>>>>>> ./scripts/config --enable CONFIG_GUP_TEST
>>>>>>>>>>>
>>>>>>>>>>> Running on VM with 12G memory, split across 2 (emulated) NUMA nodes
>>>>>>>>>>> (needed by
>>>>>>>>>>> some mm selftests), with kernel command line to reserve hugetlbs and
>>>>>>>>>>> other
>>>>>>>>>>> features required by some mm selftests:
>>>>>>>>>>>
>>>>>>>>>>> "
>>>>>>>>>>> transparent_hugepage=madvise earlycon root=/dev/vda2 secretmem.enable
>>>>>>>>>>> hugepagesz=1G hugepages=0:2,1:2 hugepagesz=32M hugepages=0:2,1:2
>>>>>>>>>>> default_hugepagesz=2M hugepages=0:64,1:64 hugepagesz=64K
>>>>>>>>>>> hugepages=0:2,1:2
>>>>>>>>>>> "
>>>>>>>>>>>
>>>>>>>>>>> Ubuntu userspace running off XFS rootfs. Build and run mm selftests
>>>>>>>>>>> from same
>>>>>>>>>>> git tree.
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Although I don't think any of this config should make a difference to
>>>>>>>>>>> gup_longterm.
>>>>>>>>>>>
>>>>>>>>>>> Looks like your errors are all "ftruncate() failed". I've seen this
>>>>>>>>>>> problem on
>>>>>>>>>>> our CI system. There it is due to running the tests from NFS file
>>>>>>>>>>> system. What
>>>>>>>>>>> filesystem are you using? Perhaps you are sharing into the FVP using
>>>>>>>>>>> 9p? That
>>>>>>>>>>> might also be problematic.
>>>>>>>>>>
>>>>>>>>>> That was it. This time I booted up the kernel including your series on
>>>>>>>>>> QEMU on my M1 and executed the gup_longterm program without the ftruncate
>>>>>>>>>> failures. When testing your kernel on FVP, I was executing the script
>>>>>>>>>> from the FVP's host filesystem using 9p.
>>>>>>>>>
>>>>>>>>> I'm not sure exactly what the root cause is. Perhaps there isn't enough
>>>>>>>>> space on
>>>>>>>>> the disk? It might be worth enhancing the error log to provide the
>>>>>>>>> errno in
>>>>>>>>> tools/testing/selftests/mm/gup_longterm.c.
>>>>>>>>>
>>>>>>>>
>>>>>>>> Attached is the strace’d gup_longterm executiong log on your
>>>>>>>> pgtable-boot-speedup-v2 kernel.
>>>>>>>
>>>>>>> Sorry are you saying that it only fails with the pgtable-boot-speedup-v2
>>>>>>> patch
>>>>>>> set applied? I thought we previously concluded that it was independent of
>>>>>>> that?
>>>>>>> I was under the impression that it was filesystem related and not something
>>>>>>> that
>>>>>>> I was planning to investigate.
>>>>>>
>>>>>> No, irrespective of the kernel, if using 9p on FVP the test program fails.
>>>>>> It is indeed 9p filesystem related, as I switched to using NFS all the
>>>>>> issues are gone.
>>>>>
>>>>> Did it never work on 9p? If so, we might have to SKIP that test.
>>>>>
>>>>> openat(AT_FDCWD, "gup_longterm.c_tmpfile_BLboOt", O_RDWR|O_CREAT|O_EXCL,
>>>>> 0600) = 3
>>>>> unlinkat(AT_FDCWD, "gup_longterm.c_tmpfile_BLboOt", 0) = 0
>>>>> fstatfs(3, 0xffffe505a840)              = -1 EOPNOTSUPP (Operation not
>>>>> supported)
>>>>> ftruncate(3, 4096)                      = -1 ENOENT (No such file or
>>>>> directory)
>>>>
>>>> Note: I'm wondering if the unlinkat here is the problem that makes
>>>> ftruncate() with 9p result in weird errors (e.g., the hypervisor
>>>> unlinked the file and cannot reopen it for the fstatfs/ftruncate. ...
>>>> which gives us weird errors here).
>>>>
>>>> Then, we should lookup the fs type in run_with_local_tmpfile() before
>>>> the unlink() and simply skip the test if it is 9p.
>>>
>>> The unlink with 9p most certainly was a known issue in the past:
>>>
>>> https://gitlab.com/qemu-project/qemu/-/issues/103
>>>
>>> Maybe it's still an issue with older hypervisors (QEMU?)? Or it was never
>>> completely resolved?
>>
>> I believe Itaru is running on FVP (Fixed Virtual Platform - "fast model" -
>> Arm's architecture emulator). So QEMU won't be involved here. The FVP emulates
>> a 9p device, so perhaps the bug is in there.
> 
> Very likely.
> 
>>
>> Note that I see lots of "fallocate() failed" failures in gup_longterm when
>> running on our CI system. This is a completely different setup; Real HW with
>> Linux running bare metal using an NFS rootfs. I'm not sure if this is related.
>> Logs show it failing consistently for the "tmpfile" and "local tmpfile" test
>> configs. I also see a couple of these fails in the cow tests.
> 
> What is the fallocate() errno you are getting? strace log would help (to see if
> statfs also fails already)! Likely a similar NFS issue.

Unfortunately this is a system I don't have access to. I've requested some of
this triage to be done, but its fairly low priority unfortunately.

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