Re: [PATCH v2 0/4] Speed up boot with faster linear map creation

[Itaru Kitayama <itaru.kitayama@linux.dev>]

> On Apr 9, 2024, at 19:04, Ryan Roberts <ryan.roberts@arm.com> wrote:
> 
> On 09/04/2024 01:10, Itaru Kitayama wrote:
>> Hi Ryan,
>> 
>>> On Apr 8, 2024, at 16:30, Ryan Roberts <ryan.roberts@arm.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.

Thanks,
Itaru.

> 
>> 
>> Thanks,
>> Itaru.
>> 
>>> Thanks,
>>> Ryan
>>> 
>>>> 
>>>> Thanks,
>>>> Itaru.
>>>> 
>>>>> 
>>>>> Does this problem reproduce with v6.9-rc2, without my patches? I except it
>>>>> probably does?
>>>>> 
>>>>> Thanks,
>>>>> Ryan
>>>>> 
>>>>>> 
>>>>>> Thanks,
>>>>>> Itaru.