From: Barry Song v-songbaohua@oppo.com
maillist inclusion category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I7U78A CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?...
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On x86, batched and deferred tlb shootdown has lead to 90% performance increase on tlb shootdown. on arm64, HW can do tlb shootdown without software IPI. But sync tlbi is still quite expensive.
Even running a simplest program which requires swapout can prove this is true, #include <sys/types.h> #include <unistd.h> #include <sys/mman.h> #include <string.h>
int main() { #define SIZE (1 * 1024 * 1024) volatile unsigned char *p = mmap(NULL, SIZE, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
memset(p, 0x88, SIZE);
for (int k = 0; k < 10000; k++) { /* swap in */ for (int i = 0; i < SIZE; i += 4096) { (void)p[i]; }
/* swap out */ madvise(p, SIZE, MADV_PAGEOUT); } }
Perf result on snapdragon 888 with 8 cores by using zRAM as the swap block device.
~ # perf record taskset -c 4 ./a.out [ perf record: Woken up 10 times to write data ] [ perf record: Captured and wrote 2.297 MB perf.data (60084 samples) ] ~ # perf report # To display the perf.data header info, please use --header/--header-only options. # To display the perf.data header info, please use --header/--header-only options. # # # Total Lost Samples: 0 # # Samples: 60K of event 'cycles' # Event count (approx.): 35706225414 # # Overhead Command Shared Object Symbol # ........ ....... ................. ...... # 21.07% a.out [kernel.kallsyms] [k] _raw_spin_unlock_irq 8.23% a.out [kernel.kallsyms] [k] _raw_spin_unlock_irqrestore 6.67% a.out [kernel.kallsyms] [k] filemap_map_pages 6.16% a.out [kernel.kallsyms] [k] __zram_bvec_write 5.36% a.out [kernel.kallsyms] [k] ptep_clear_flush 3.71% a.out [kernel.kallsyms] [k] _raw_spin_lock 3.49% a.out [kernel.kallsyms] [k] memset64 1.63% a.out [kernel.kallsyms] [k] clear_page 1.42% a.out [kernel.kallsyms] [k] _raw_spin_unlock 1.26% a.out [kernel.kallsyms] [k] mod_zone_state.llvm.8525150236079521930 1.23% a.out [kernel.kallsyms] [k] xas_load 1.15% a.out [kernel.kallsyms] [k] zram_slot_lock
ptep_clear_flush() takes 5.36% CPU in the micro-benchmark swapping in/out a page mapped by only one process. If the page is mapped by multiple processes, typically, like more than 100 on a phone, the overhead would be much higher as we have to run tlb flush 100 times for one single page. Plus, tlb flush overhead will increase with the number of CPU cores due to the bad scalability of tlb shootdown in HW, so those ARM64 servers should expect much higher overhead.
Further perf annonate shows 95% cpu time of ptep_clear_flush is actually used by the final dsb() to wait for the completion of tlb flush. This provides us a very good chance to leverage the existing batched tlb in kernel. The minimum modification is that we only send async tlbi in the first stage and we send dsb while we have to sync in the second stage.
With the above simplest micro benchmark, collapsed time to finish the program decreases around 5%.
Typical collapsed time w/o patch: ~ # time taskset -c 4 ./a.out 0.21user 14.34system 0:14.69elapsed w/ patch: ~ # time taskset -c 4 ./a.out 0.22user 13.45system 0:13.80elapsed
Also tested with benchmark in the commit on Kunpeng920 arm64 server and observed an improvement around 12.5% with command `time ./swap_bench`. w/o w/ real 0m13.460s 0m11.771s user 0m0.248s 0m0.279s sys 0m12.039s 0m11.458s
Originally it's noticed a 16.99% overhead of ptep_clear_flush() which has been eliminated by this patch:
[root@localhost yang]# perf record -- ./swap_bench && perf report [...] 16.99% swap_bench [kernel.kallsyms] [k] ptep_clear_flush
It is tested on 4,8,128 CPU platforms and shows to be beneficial on large systems but may not have improvement on small systems like on a 4 CPU platform.
Also this patch improve the performance of page migration. Using pmbench and tries to migrate the pages of pmbench between node 0 and node 1 for 100 times for 1G memory, this patch decrease the time used around 20% (prev 18.338318910 sec after 13.981866350 sec) and saved the time used by ptep_clear_flush().
Link: https://lkml.kernel.org/r/20230717131004.12662-5-yangyicong@huawei.com Tested-by: Yicong Yang yangyicong@hisilicon.com Tested-by: Xin Hao xhao@linux.alibaba.com Tested-by: Punit Agrawal punit.agrawal@bytedance.com Signed-off-by: Barry Song v-songbaohua@oppo.com Signed-off-by: Yicong Yang yangyicong@hisilicon.com Reviewed-by: Kefeng Wang wangkefeng.wang@huawei.com Reviewed-by: Xin Hao xhao@linux.alibaba.com Reviewed-by: Anshuman Khandual anshuman.khandual@arm.com Reviewed-by: Catalin Marinas catalin.marinas@arm.com Cc: Anshuman Khandual anshuman.khandual@arm.com Cc: Jonathan Corbet corbet@lwn.net Cc: Nadav Amit namit@vmware.com Cc: Mel Gorman mgorman@suse.de Cc: Anshuman Khandual khandual@linux.vnet.ibm.com Cc: Arnd Bergmann arnd@arndb.de Cc: Barry Song baohua@kernel.org Cc: Darren Hart darren@os.amperecomputing.com Cc: Jonathan Cameron Jonathan.Cameron@huawei.com Cc: lipeifeng lipeifeng@oppo.com Cc: Mark Rutland mark.rutland@arm.com Cc: Peter Zijlstra peterz@infradead.org Cc: Ryan Roberts ryan.roberts@arm.com Cc: Steven Miao realmz6@gmail.com Cc: Will Deacon will@kernel.org Cc: Zeng Tao prime.zeng@hisilicon.com Signed-off-by: Andrew Morton akpm@linux-foundation.org
Conflicts: Documentation/features/vm/TLB/arch-support.txt arch/arm64/Kconfig
fix kabi breakage for mm_struct->tlb_flush_batched
Signed-off-by: Jinjiang Tu tujinjiang@huawei.com --- .../features/vm/TLB/arch-support.txt | 2 +- arch/arm64/Kconfig | 1 + arch/arm64/include/asm/tlbbatch.h | 12 +++++ arch/arm64/include/asm/tlbflush.h | 44 +++++++++++++++++-- include/linux/mm_types.h | 4 +- 5 files changed, 58 insertions(+), 5 deletions(-) create mode 100644 arch/arm64/include/asm/tlbbatch.h
diff --git a/Documentation/features/vm/TLB/arch-support.txt b/Documentation/features/vm/TLB/arch-support.txt index 30f75a79ce01..1ccf586c7810 100644 --- a/Documentation/features/vm/TLB/arch-support.txt +++ b/Documentation/features/vm/TLB/arch-support.txt @@ -9,7 +9,7 @@ | alpha: | TODO | | arc: | TODO | | arm: | TODO | - | arm64: | TODO | + | arm64: | ok | | c6x: | .. | | csky: | TODO | | h8300: | .. | diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 16620146c49a..139d98a7a12d 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -78,6 +78,7 @@ config ARM64 select ARCH_SUPPORTS_ATOMIC_RMW select ARCH_SUPPORTS_INT128 if CC_HAS_INT128 && (GCC_VERSION >= 50000 || CC_IS_CLANG) select ARCH_SUPPORTS_NUMA_BALANCING + select ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH select ARCH_WANT_COMPAT_IPC_PARSE_VERSION if COMPAT select ARCH_WANT_DEFAULT_BPF_JIT select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT diff --git a/arch/arm64/include/asm/tlbbatch.h b/arch/arm64/include/asm/tlbbatch.h new file mode 100644 index 000000000000..fedb0b87b8db --- /dev/null +++ b/arch/arm64/include/asm/tlbbatch.h @@ -0,0 +1,12 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _ARCH_ARM64_TLBBATCH_H +#define _ARCH_ARM64_TLBBATCH_H + +struct arch_tlbflush_unmap_batch { + /* + * For arm64, HW can do tlb shootdown, so we don't + * need to record cpumask for sending IPI + */ +}; + +#endif /* _ARCH_ARM64_TLBBATCH_H */ diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h index 36f02892e1df..4c28c6c4acba 100644 --- a/arch/arm64/include/asm/tlbflush.h +++ b/arch/arm64/include/asm/tlbflush.h @@ -254,17 +254,23 @@ static inline void flush_tlb_mm(struct mm_struct *mm) dsb(ish); }
-static inline void flush_tlb_page_nosync(struct vm_area_struct *vma, - unsigned long uaddr) +static inline void __flush_tlb_page_nosync(struct mm_struct *mm, + unsigned long uaddr) { unsigned long addr;
dsb(ishst); - addr = __TLBI_VADDR(uaddr, ASID(vma->vm_mm)); + addr = __TLBI_VADDR(uaddr, ASID(mm)); __tlbi(vale1is, addr); __tlbi_user(vale1is, addr); }
+static inline void flush_tlb_page_nosync(struct vm_area_struct *vma, + unsigned long uaddr) +{ + return __flush_tlb_page_nosync(vma->vm_mm, uaddr); +} + static inline void flush_tlb_page(struct vm_area_struct *vma, unsigned long uaddr) { @@ -272,6 +278,38 @@ static inline void flush_tlb_page(struct vm_area_struct *vma, dsb(ish); }
+static inline bool arch_tlbbatch_should_defer(struct mm_struct *mm) +{ +#ifdef CONFIG_ARM64_WORKAROUND_REPEAT_TLBI + /* + * TLB flush deferral is not required on systems which are affected by + * ARM64_WORKAROUND_REPEAT_TLBI, as __tlbi()/__tlbi_user() implementation + * will have two consecutive TLBI instructions with a dsb(ish) in between + * defeating the purpose (i.e save overall 'dsb ish' cost). + */ + if (unlikely(cpus_have_const_cap(ARM64_WORKAROUND_REPEAT_TLBI))) + return false; +#endif + return true; +} + +static inline void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_batch *batch, + struct mm_struct *mm, + unsigned long uaddr) +{ + __flush_tlb_page_nosync(mm, uaddr); +} + +static inline void arch_flush_tlb_batched_pending(struct mm_struct *mm) +{ + dsb(ish); +} + +static inline void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch) +{ + dsb(ish); +} + /* * This is meant to avoid soft lock-ups on large TLB flushing ranges and not * necessarily a performance improvement. diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index e3eaf458787a..d1be389c0468 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -598,7 +598,7 @@ struct mm_struct { * moving a PROT_NONE or PROT_NUMA mapped page. */ atomic_t tlb_flush_pending; -#ifdef CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH +#if defined(CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH) && !defined(CONFIG_ARM64) /* See flush_tlb_batched_pending() */ bool tlb_flush_batched; #endif @@ -620,6 +620,8 @@ struct mm_struct {
#if defined(CONFIG_X86_64) KABI_USE(1, struct mm_struct_extend *mm_extend) +#elif defined(CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH) && defined(CONFIG_ARM64) + KABI_USE(1, bool tlb_flush_batched) #else KABI_RESERVE(1) #endif