Re: [v5,22/22] powerpc/mm: Add speculative page fault

From: kemi
Date: Thu Oct 26 2017 - 04:16:24 EST

Some regression is found by LKP-tools(linux kernel performance) on this patch series
tested on Intel 2s/4s Skylake platform.
The regression result is sorted by the metric will-it-scale.per_process_ops.

Branch:Laurent-Dufour/Speculative-page-faults/20171011-213456(V4 patch series)
Commit id:
base:9a4b4dd1d8700dd5771f11dd2c048e4363efb493
head:56a4a8962fb32555a42eefdc9a19eeedd3e8c2e6
Benchmark suite:will-it-scale
Download link:https://github.com/antonblanchard/will-it-scale/tree/master/tests
Metrics:
will-it-scale.per_process_ops=processes/nr_cpu
will-it-scale.per_thread_ops=threads/nr_cpu

tbox:lkp-skl-4sp1(nr_cpu=192,memory=768G)
kconfig:CONFIG_TRANSPARENT_HUGEPAGE is not set
testcase base change head metric
brk1 2251803 -18.1% 1843535 will-it-scale.per_process_ops
341101 -17.5% 281284 will-it-scale.per_thread_ops
malloc1 48833 -9.2% 44343 will-it-scale.per_process_ops
31555 +2.9% 32473 will-it-scale.per_thread_ops
page_fault3 913019 -8.5% 835203 will-it-scale.per_process_ops
233978 -18.1% 191593 will-it-scale.per_thread_ops
mmap2 95892 -6.6% 89536 will-it-scale.per_process_ops
90180 -13.7% 77803 will-it-scale.per_thread_ops
mmap1 109586 -4.7% 104414 will-it-scale.per_process_ops
104477 -12.4% 91484 will-it-scale.per_thread_ops
sched_yield 4964649 -2.1% 4859927 will-it-scale.per_process_ops
4946759 -1.7% 4864924 will-it-scale.per_thread_ops
write1 1345159 -1.3% 1327719 will-it-scale.per_process_ops
1228754 -2.2% 1201915 will-it-scale.per_thread_ops
page_fault2 202519 -1.0% 200545 will-it-scale.per_process_ops
96573 -10.4% 86526 will-it-scale.per_thread_ops
page_fault1 225608 -0.9% 223585 will-it-scale.per_process_ops
105945 +14.4% 121199 will-it-scale.per_thread_ops

tbox:lkp-skl-4sp1(nr_cpu=192,memory=768G)
kconfig:CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y
testcase base change head metric
context_switch1 333780 -23.0% 256927 will-it-scale.per_process_ops
brk1 2263539 -18.8% 1837462 will-it-scale.per_process_ops
325854 -15.7% 274752 will-it-scale.per_thread_ops
malloc1 48746 -13.5% 42148 will-it-scale.per_process_ops
mmap1 106860 -12.4% 93634 will-it-scale.per_process_ops
98082 -18.9% 79506 will-it-scale.per_thread_ops
mmap2 92468 -11.3% 82059 will-it-scale.per_process_ops
80468 -8.9% 73343 will-it-scale.per_thread_ops
page_fault3 900709 -9.1% 818851 will-it-scale.per_process_ops
229837 -18.3% 187769 will-it-scale.per_thread_ops
write1 1327409 -1.7% 1305048 will-it-scale.per_process_ops
1215658 -1.6% 1196479 will-it-scale.per_thread_ops
writeseek3 300639 -1.6% 295882 will-it-scale.per_process_ops
231118 -2.2% 225929 will-it-scale.per_thread_ops
signal1 122011 -1.5% 120155 will-it-scale.per_process_ops
futex1 5123778 -1.2% 5062087 will-it-scale.per_process_ops
page_fault2 202321 -1.0% 200289 will-it-scale.per_process_ops
93073 -9.8% 83927 will-it-scale.per_thread_ops

tbox:lkp-skl-2sp2(nr_cpu=112,memory=64G)
kconfig:CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y
testcase base change head metric
brk1 2177903 -20.0% 1742054 will-it-scale.per_process_ops
434558 -15.3% 367896 will-it-scale.per_thread_ops
malloc1 64871 -10.3% 58174 will-it-scale.per_process_ops
page_fault3 882435 -9.0% 802892 will-it-scale.per_process_ops
299176 -15.7% 252170 will-it-scale.per_thread_ops
mmap2 124567 -8.3% 114214 will-it-scale.per_process_ops
110674 -12.1% 97272 will-it-scale.per_thread_ops
mmap1 137205 -7.8% 126440 will-it-scale.per_process_ops
128973 -15.1% 109560 will-it-scale.per_thread_ops
context_switch1 343790 -7.2% 319209 will-it-scale.per_process_ops
page_fault2 161891 -2.1% 158458 will-it-scale.per_process_ops
123278 -5.4% 116629 will-it-scale.per_thread_ops
malloc2 14354856 -1.8% 14096856 will-it-scale.per_process_ops
read2 1204838 -1.7% 1183993 will-it-scale.per_process_ops
futex1 5017718 -1.6% 4938677 will-it-scale.per_process_ops
1408250 -1.0% 1394022 will-it-scale.per_thread_ops
writeseek3 399651 -1.4% 393935 will-it-scale.per_process_ops
signal1 157952 -1.0% 156302 will-it-scale.per_process_ops

On 2017å10æ11æ 21:52, Laurent Dufour wrote:
> This patch enable the speculative page fault on the PowerPC
> architecture.
>
> This will try a speculative page fault without holding the mmap_sem,
> if it returns with VM_FAULT_RETRY, the mmap_sem is acquired and the
> traditional page fault processing is done.
>
> Build on if CONFIG_SPF is defined (currently for BOOK3S_64 && SMP).
>
> Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx>
> ---
> arch/powerpc/mm/fault.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 4797d08581ce..c018c2554cc8 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -442,6 +442,20 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
> if (is_exec)
> flags |= FAULT_FLAG_INSTRUCTION;
>
> +#ifdef CONFIG_SPF
> + if (is_user) {
> + /* let's try a speculative page fault without grabbing the
> + * mmap_sem.
> + */
> + fault = handle_speculative_fault(mm, address, flags);
> + if (!(fault & VM_FAULT_RETRY)) {
> + perf_sw_event(PERF_COUNT_SW_SPF, 1,
> + regs, address);
> + goto done;
> + }
> + }
> +#endif /* CONFIG_SPF */
> +
> /* When running in the kernel we expect faults to occur only to
> * addresses in user space. All other faults represent errors in the
> * kernel and should generate an OOPS. Unfortunately, in the case of an
> @@ -526,6 +540,9 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
>
> up_read(&current->mm->mmap_sem);
>
> +#ifdef CONFIG_SPF
> +done:
> +#endif
> if (unlikely(fault & VM_FAULT_ERROR))
> return mm_fault_error(regs, address, fault);
>
>