[PATCH v11 00/26] Speculative page faults
Haiyan Song
haiyanx.song at intel.com
Mon May 28 18:22:36 AEST 2018
Hi Laurent,
Yes, these tests are done on V9 patch.
Best regards,
Haiyan Song
On Mon, May 28, 2018 at 09:51:34AM +0200, Laurent Dufour wrote:
> On 28/05/2018 07:23, Song, HaiyanX wrote:
> >
> > Some regression and improvements is found by LKP-tools(linux kernel performance) on V9 patch series
> > tested on Intel 4s Skylake platform.
>
> Hi,
>
> Thanks for reporting this benchmark results, but you mentioned the "V9 patch
> series" while responding to the v11 header series...
> Were these tests done on v9 or v11 ?
>
> Cheers,
> Laurent.
>
> >
> > The regression result is sorted by the metric will-it-scale.per_thread_ops.
> > Branch: Laurent-Dufour/Speculative-page-faults/20180316-151833 (V9 patch series)
> > Commit id:
> > base commit: d55f34411b1b126429a823d06c3124c16283231f
> > head commit: 0355322b3577eeab7669066df42c550a56801110
> > 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
> > test box: lkp-skl-4sp1(nr_cpu=192,memory=768G)
> > THP: enable / disable
> > nr_task: 100%
> >
> > 1. Regressions:
> > a) THP enabled:
> > testcase base change head metric
> > page_fault3/ enable THP 10092 -17.5% 8323 will-it-scale.per_thread_ops
> > page_fault2/ enable THP 8300 -17.2% 6869 will-it-scale.per_thread_ops
> > brk1/ enable THP 957.67 -7.6% 885 will-it-scale.per_thread_ops
> > page_fault3/ enable THP 172821 -5.3% 163692 will-it-scale.per_process_ops
> > signal1/ enable THP 9125 -3.2% 8834 will-it-scale.per_process_ops
> >
> > b) THP disabled:
> > testcase base change head metric
> > page_fault3/ disable THP 10107 -19.1% 8180 will-it-scale.per_thread_ops
> > page_fault2/ disable THP 8432 -17.8% 6931 will-it-scale.per_thread_ops
> > context_switch1/ disable THP 215389 -6.8% 200776 will-it-scale.per_thread_ops
> > brk1/ disable THP 939.67 -6.6% 877.33 will-it-scale.per_thread_ops
> > page_fault3/ disable THP 173145 -4.7% 165064 will-it-scale.per_process_ops
> > signal1/ disable THP 9162 -3.9% 8802 will-it-scale.per_process_ops
> >
> > 2. Improvements:
> > a) THP enabled:
> > testcase base change head metric
> > malloc1/ enable THP 66.33 +469.8% 383.67 will-it-scale.per_thread_ops
> > writeseek3/ enable THP 2531 +4.5% 2646 will-it-scale.per_thread_ops
> > signal1/ enable THP 989.33 +2.8% 1016 will-it-scale.per_thread_ops
> >
> > b) THP disabled:
> > testcase base change head metric
> > malloc1/ disable THP 90.33 +417.3% 467.33 will-it-scale.per_thread_ops
> > read2/ disable THP 58934 +39.2% 82060 will-it-scale.per_thread_ops
> > page_fault1/ disable THP 8607 +36.4% 11736 will-it-scale.per_thread_ops
> > read1/ disable THP 314063 +12.7% 353934 will-it-scale.per_thread_ops
> > writeseek3/ disable THP 2452 +12.5% 2759 will-it-scale.per_thread_ops
> > signal1/ disable THP 971.33 +5.5% 1024 will-it-scale.per_thread_ops
> >
> > Notes: for above values in column "change", the higher value means that the related testcase result
> > on head commit is better than that on base commit for this benchmark.
> >
> >
> > Best regards
> > Haiyan Song
> >
> > ________________________________________
> > From: owner-linux-mm at kvack.org [owner-linux-mm at kvack.org] on behalf of Laurent Dufour [ldufour at linux.vnet.ibm.com]
> > Sent: Thursday, May 17, 2018 7:06 PM
> > To: akpm at linux-foundation.org; mhocko at kernel.org; peterz at infradead.org; kirill at shutemov.name; ak at linux.intel.com; dave at stgolabs.net; jack at suse.cz; Matthew Wilcox; khandual at linux.vnet.ibm.com; aneesh.kumar at linux.vnet.ibm.com; benh at kernel.crashing.org; mpe at ellerman.id.au; paulus at samba.org; Thomas Gleixner; Ingo Molnar; hpa at zytor.com; Will Deacon; Sergey Senozhatsky; sergey.senozhatsky.work at gmail.com; Andrea Arcangeli; Alexei Starovoitov; Wang, Kemi; Daniel Jordan; David Rientjes; Jerome Glisse; Ganesh Mahendran; Minchan Kim; Punit Agrawal; vinayak menon; Yang Shi
> > Cc: linux-kernel at vger.kernel.org; linux-mm at kvack.org; haren at linux.vnet.ibm.com; npiggin at gmail.com; bsingharora at gmail.com; paulmck at linux.vnet.ibm.com; Tim Chen; linuxppc-dev at lists.ozlabs.org; x86 at kernel.org
> > Subject: [PATCH v11 00/26] Speculative page faults
> >
> > This is a port on kernel 4.17 of the work done by Peter Zijlstra to handle
> > page fault without holding the mm semaphore [1].
> >
> > The idea is to try to handle user space page faults without holding the
> > mmap_sem. This should allow better concurrency for massively threaded
> > process since the page fault handler will not wait for other threads memory
> > layout change to be done, assuming that this change is done in another part
> > of the process's memory space. This type page fault is named speculative
> > page fault. If the speculative page fault fails because of a concurrency is
> > detected or because underlying PMD or PTE tables are not yet allocating, it
> > is failing its processing and a classic page fault is then tried.
> >
> > The speculative page fault (SPF) has to look for the VMA matching the fault
> > address without holding the mmap_sem, this is done by introducing a rwlock
> > which protects the access to the mm_rb tree. Previously this was done using
> > SRCU but it was introducing a lot of scheduling to process the VMA's
> > freeing operation which was hitting the performance by 20% as reported by
> > Kemi Wang [2]. Using a rwlock to protect access to the mm_rb tree is
> > limiting the locking contention to these operations which are expected to
> > be in a O(log n) order. In addition to ensure that the VMA is not freed in
> > our back a reference count is added and 2 services (get_vma() and
> > put_vma()) are introduced to handle the reference count. Once a VMA is
> > fetched from the RB tree using get_vma(), it must be later freed using
> > put_vma(). I can't see anymore the overhead I got while will-it-scale
> > benchmark anymore.
> >
> > The VMA's attributes checked during the speculative page fault processing
> > have to be protected against parallel changes. This is done by using a per
> > VMA sequence lock. This sequence lock allows the speculative page fault
> > handler to fast check for parallel changes in progress and to abort the
> > speculative page fault in that case.
> >
> > Once the VMA has been found, the speculative page fault handler would check
> > for the VMA's attributes to verify that the page fault has to be handled
> > correctly or not. Thus, the VMA is protected through a sequence lock which
> > allows fast detection of concurrent VMA changes. If such a change is
> > detected, the speculative page fault is aborted and a *classic* page fault
> > is tried. VMA sequence lockings are added when VMA attributes which are
> > checked during the page fault are modified.
> >
> > When the PTE is fetched, the VMA is checked to see if it has been changed,
> > so once the page table is locked, the VMA is valid, so any other changes
> > leading to touching this PTE will need to lock the page table, so no
> > parallel change is possible at this time.
> >
> > The locking of the PTE is done with interrupts disabled, this allows
> > checking for the PMD to ensure that there is not an ongoing collapsing
> > operation. Since khugepaged is firstly set the PMD to pmd_none and then is
> > waiting for the other CPU to have caught the IPI interrupt, if the pmd is
> > valid at the time the PTE is locked, we have the guarantee that the
> > collapsing operation will have to wait on the PTE lock to move forward.
> > This allows the SPF handler to map the PTE safely. If the PMD value is
> > different from the one recorded at the beginning of the SPF operation, the
> > classic page fault handler will be called to handle the operation while
> > holding the mmap_sem. As the PTE lock is done with the interrupts disabled,
> > the lock is done using spin_trylock() to avoid dead lock when handling a
> > page fault while a TLB invalidate is requested by another CPU holding the
> > PTE.
> >
> > In pseudo code, this could be seen as:
> > speculative_page_fault()
> > {
> > vma = get_vma()
> > check vma sequence count
> > check vma's support
> > disable interrupt
> > check pgd,p4d,...,pte
> > save pmd and pte in vmf
> > save vma sequence counter in vmf
> > enable interrupt
> > check vma sequence count
> > handle_pte_fault(vma)
> > ..
> > page = alloc_page()
> > pte_map_lock()
> > disable interrupt
> > abort if sequence counter has changed
> > abort if pmd or pte has changed
> > pte map and lock
> > enable interrupt
> > if abort
> > free page
> > abort
> > ...
> > }
> >
> > arch_fault_handler()
> > {
> > if (speculative_page_fault(&vma))
> > goto done
> > again:
> > lock(mmap_sem)
> > vma = find_vma();
> > handle_pte_fault(vma);
> > if retry
> > unlock(mmap_sem)
> > goto again;
> > done:
> > handle fault error
> > }
> >
> > Support for THP is not done because when checking for the PMD, we can be
> > confused by an in progress collapsing operation done by khugepaged. The
> > issue is that pmd_none() could be true either if the PMD is not already
> > populated or if the underlying PTE are in the way to be collapsed. So we
> > cannot safely allocate a PMD if pmd_none() is true.
> >
> > This series add a new software performance event named 'speculative-faults'
> > or 'spf'. It counts the number of successful page fault event handled
> > speculatively. When recording 'faults,spf' events, the faults one is
> > counting the total number of page fault events while 'spf' is only counting
> > the part of the faults processed speculatively.
> >
> > There are some trace events introduced by this series. They allow
> > identifying why the page faults were not processed speculatively. This
> > doesn't take in account the faults generated by a monothreaded process
> > which directly processed while holding the mmap_sem. This trace events are
> > grouped in a system named 'pagefault', they are:
> > - pagefault:spf_vma_changed : if the VMA has been changed in our back
> > - pagefault:spf_vma_noanon : the vma->anon_vma field was not yet set.
> > - pagefault:spf_vma_notsup : the VMA's type is not supported
> > - pagefault:spf_vma_access : the VMA's access right are not respected
> > - pagefault:spf_pmd_changed : the upper PMD pointer has changed in our
> > back.
> >
> > To record all the related events, the easier is to run perf with the
> > following arguments :
> > $ perf stat -e 'faults,spf,pagefault:*' <command>
> >
> > There is also a dedicated vmstat counter showing the number of successful
> > page fault handled speculatively. I can be seen this way:
> > $ grep speculative_pgfault /proc/vmstat
> >
> > This series builds on top of v4.16-mmotm-2018-04-13-17-28 and is functional
> > on x86, PowerPC and arm64.
> >
> > ---------------------
> > Real Workload results
> >
> > As mentioned in previous email, we did non official runs using a "popular
> > in memory multithreaded database product" on 176 cores SMT8 Power system
> > which showed a 30% improvements in the number of transaction processed per
> > second. This run has been done on the v6 series, but changes introduced in
> > this new version should not impact the performance boost seen.
> >
> > Here are the perf data captured during 2 of these runs on top of the v8
> > series:
> > vanilla spf
> > faults 89.418 101.364 +13%
> > spf n/a 97.989
> >
> > With the SPF kernel, most of the page fault were processed in a speculative
> > way.
> >
> > Ganesh Mahendran had backported the series on top of a 4.9 kernel and gave
> > it a try on an android device. He reported that the application launch time
> > was improved in average by 6%, and for large applications (~100 threads) by
> > 20%.
> >
> > Here are the launch time Ganesh mesured on Android 8.0 on top of a Qcom
> > MSM845 (8 cores) with 6GB (the less is better):
> >
> > Application 4.9 4.9+spf delta
> > com.tencent.mm 416 389 -7%
> > com.eg.android.AlipayGphone 1135 986 -13%
> > com.tencent.mtt 455 454 0%
> > com.qqgame.hlddz 1497 1409 -6%
> > com.autonavi.minimap 711 701 -1%
> > com.tencent.tmgp.sgame 788 748 -5%
> > com.immomo.momo 501 487 -3%
> > com.tencent.peng 2145 2112 -2%
> > com.smile.gifmaker 491 461 -6%
> > com.baidu.BaiduMap 479 366 -23%
> > com.taobao.taobao 1341 1198 -11%
> > com.baidu.searchbox 333 314 -6%
> > com.tencent.mobileqq 394 384 -3%
> > com.sina.weibo 907 906 0%
> > com.youku.phone 816 731 -11%
> > com.happyelements.AndroidAnimal.qq 763 717 -6%
> > com.UCMobile 415 411 -1%
> > com.tencent.tmgp.ak 1464 1431 -2%
> > com.tencent.qqmusic 336 329 -2%
> > com.sankuai.meituan 1661 1302 -22%
> > com.netease.cloudmusic 1193 1200 1%
> > air.tv.douyu.android 4257 4152 -2%
> >
> > ------------------
> > Benchmarks results
> >
> > Base kernel is v4.17.0-rc4-mm1
> > SPF is BASE + this series
> >
> > Kernbench:
> > ----------
> > Here are the results on a 16 CPUs X86 guest using kernbench on a 4.15
> > kernel (kernel is build 5 times):
> >
> > Average Half load -j 8
> > Run (std deviation)
> > BASE SPF
> > Elapsed Time 1448.65 (5.72312) 1455.84 (4.84951) 0.50%
> > User Time 10135.4 (30.3699) 10148.8 (31.1252) 0.13%
> > System Time 900.47 (2.81131) 923.28 (7.52779) 2.53%
> > Percent CPU 761.4 (1.14018) 760.2 (0.447214) -0.16%
> > Context Switches 85380 (3419.52) 84748 (1904.44) -0.74%
> > Sleeps 105064 (1240.96) 105074 (337.612) 0.01%
> >
> > Average Optimal load -j 16
> > Run (std deviation)
> > BASE SPF
> > Elapsed Time 920.528 (10.1212) 927.404 (8.91789) 0.75%
> > User Time 11064.8 (981.142) 11085 (990.897) 0.18%
> > System Time 979.904 (84.0615) 1001.14 (82.5523) 2.17%
> > Percent CPU 1089.5 (345.894) 1086.1 (343.545) -0.31%
> > Context Switches 159488 (78156.4) 158223 (77472.1) -0.79%
> > Sleeps 110566 (5877.49) 110388 (5617.75) -0.16%
> >
> >
> > During a run on the SPF, perf events were captured:
> > Performance counter stats for '../kernbench -M':
> > 526743764 faults
> > 210 spf
> > 3 pagefault:spf_vma_changed
> > 0 pagefault:spf_vma_noanon
> > 2278 pagefault:spf_vma_notsup
> > 0 pagefault:spf_vma_access
> > 0 pagefault:spf_pmd_changed
> >
> > Very few speculative page faults were recorded as most of the processes
> > involved are monothreaded (sounds that on this architecture some threads
> > were created during the kernel build processing).
> >
> > Here are the kerbench results on a 80 CPUs Power8 system:
> >
> > Average Half load -j 40
> > Run (std deviation)
> > BASE SPF
> > Elapsed Time 117.152 (0.774642) 117.166 (0.476057) 0.01%
> > User Time 4478.52 (24.7688) 4479.76 (9.08555) 0.03%
> > System Time 131.104 (0.720056) 134.04 (0.708414) 2.24%
> > Percent CPU 3934 (19.7104) 3937.2 (19.0184) 0.08%
> > Context Switches 92125.4 (576.787) 92581.6 (198.622) 0.50%
> > Sleeps 317923 (652.499) 318469 (1255.59) 0.17%
> >
> > Average Optimal load -j 80
> > Run (std deviation)
> > BASE SPF
> > Elapsed Time 107.73 (0.632416) 107.31 (0.584936) -0.39%
> > User Time 5869.86 (1466.72) 5871.71 (1467.27) 0.03%
> > System Time 153.728 (23.8573) 157.153 (24.3704) 2.23%
> > Percent CPU 5418.6 (1565.17) 5436.7 (1580.91) 0.33%
> > Context Switches 223861 (138865) 225032 (139632) 0.52%
> > Sleeps 330529 (13495.1) 332001 (14746.2) 0.45%
> >
> > During a run on the SPF, perf events were captured:
> > Performance counter stats for '../kernbench -M':
> > 116730856 faults
> > 0 spf
> > 3 pagefault:spf_vma_changed
> > 0 pagefault:spf_vma_noanon
> > 476 pagefault:spf_vma_notsup
> > 0 pagefault:spf_vma_access
> > 0 pagefault:spf_pmd_changed
> >
> > Most of the processes involved are monothreaded so SPF is not activated but
> > there is no impact on the performance.
> >
> > Ebizzy:
> > -------
> > The test is counting the number of records per second it can manage, the
> > higher is the best. I run it like this 'ebizzy -mTt <nrcpus>'. To get
> > consistent result I repeated the test 100 times and measure the average
> > result. The number is the record processes per second, the higher is the
> > best.
> >
> > BASE SPF delta
> > 16 CPUs x86 VM 742.57 1490.24 100.69%
> > 80 CPUs P8 node 13105.4 24174.23 84.46%
> >
> > Here are the performance counter read during a run on a 16 CPUs x86 VM:
> > Performance counter stats for './ebizzy -mTt 16':
> > 1706379 faults
> > 1674599 spf
> > 30588 pagefault:spf_vma_changed
> > 0 pagefault:spf_vma_noanon
> > 363 pagefault:spf_vma_notsup
> > 0 pagefault:spf_vma_access
> > 0 pagefault:spf_pmd_changed
> >
> > And the ones captured during a run on a 80 CPUs Power node:
> > Performance counter stats for './ebizzy -mTt 80':
> > 1874773 faults
> > 1461153 spf
> > 413293 pagefault:spf_vma_changed
> > 0 pagefault:spf_vma_noanon
> > 200 pagefault:spf_vma_notsup
> > 0 pagefault:spf_vma_access
> > 0 pagefault:spf_pmd_changed
> >
> > In ebizzy's case most of the page fault were handled in a speculative way,
> > leading the ebizzy performance boost.
> >
> > ------------------
> > Changes since v10 (https://lkml.org/lkml/2018/4/17/572):
> > - Accounted for all review feedbacks from Punit Agrawal, Ganesh Mahendran
> > and Minchan Kim, hopefully.
> > - Remove unneeded check on CONFIG_SPECULATIVE_PAGE_FAULT in
> > __do_page_fault().
> > - Loop in pte_spinlock() and pte_map_lock() when pte try lock fails
> > instead
> > of aborting the speculative page fault handling. Dropping the now
> > useless
> > trace event pagefault:spf_pte_lock.
> > - No more try to reuse the fetched VMA during the speculative page fault
> > handling when retrying is needed. This adds a lot of complexity and
> > additional tests done didn't show a significant performance improvement.
> > - Convert IS_ENABLED(CONFIG_NUMA) back to #ifdef due to build error.
> >
> > [1] http://linux-kernel.2935.n7.nabble.com/RFC-PATCH-0-6-Another-go-at-speculative-page-faults-tt965642.html#none
> > [2] https://patchwork.kernel.org/patch/9999687/
> >
> >
> > Laurent Dufour (20):
> > mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT
> > x86/mm: define ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
> > powerpc/mm: set ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
> > mm: introduce pte_spinlock for FAULT_FLAG_SPECULATIVE
> > mm: make pte_unmap_same compatible with SPF
> > mm: introduce INIT_VMA()
> > mm: protect VMA modifications using VMA sequence count
> > mm: protect mremap() against SPF hanlder
> > mm: protect SPF handler against anon_vma changes
> > mm: cache some VMA fields in the vm_fault structure
> > mm/migrate: Pass vm_fault pointer to migrate_misplaced_page()
> > mm: introduce __lru_cache_add_active_or_unevictable
> > mm: introduce __vm_normal_page()
> > mm: introduce __page_add_new_anon_rmap()
> > mm: protect mm_rb tree with a rwlock
> > mm: adding speculative page fault failure trace events
> > perf: add a speculative page fault sw event
> > perf tools: add support for the SPF perf event
> > mm: add speculative page fault vmstats
> > powerpc/mm: add speculative page fault
> >
> > Mahendran Ganesh (2):
> > arm64/mm: define ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
> > arm64/mm: add speculative page fault
> >
> > Peter Zijlstra (4):
> > mm: prepare for FAULT_FLAG_SPECULATIVE
> > mm: VMA sequence count
> > mm: provide speculative fault infrastructure
> > x86/mm: add speculative pagefault handling
> >
> > arch/arm64/Kconfig | 1 +
> > arch/arm64/mm/fault.c | 12 +
> > arch/powerpc/Kconfig | 1 +
> > arch/powerpc/mm/fault.c | 16 +
> > arch/x86/Kconfig | 1 +
> > arch/x86/mm/fault.c | 27 +-
> > fs/exec.c | 2 +-
> > fs/proc/task_mmu.c | 5 +-
> > fs/userfaultfd.c | 17 +-
> > include/linux/hugetlb_inline.h | 2 +-
> > include/linux/migrate.h | 4 +-
> > include/linux/mm.h | 136 +++++++-
> > include/linux/mm_types.h | 7 +
> > include/linux/pagemap.h | 4 +-
> > include/linux/rmap.h | 12 +-
> > include/linux/swap.h | 10 +-
> > include/linux/vm_event_item.h | 3 +
> > include/trace/events/pagefault.h | 80 +++++
> > include/uapi/linux/perf_event.h | 1 +
> > kernel/fork.c | 5 +-
> > mm/Kconfig | 22 ++
> > mm/huge_memory.c | 6 +-
> > mm/hugetlb.c | 2 +
> > mm/init-mm.c | 3 +
> > mm/internal.h | 20 ++
> > mm/khugepaged.c | 5 +
> > mm/madvise.c | 6 +-
> > mm/memory.c | 612 +++++++++++++++++++++++++++++-----
> > mm/mempolicy.c | 51 ++-
> > mm/migrate.c | 6 +-
> > mm/mlock.c | 13 +-
> > mm/mmap.c | 229 ++++++++++---
> > mm/mprotect.c | 4 +-
> > mm/mremap.c | 13 +
> > mm/nommu.c | 2 +-
> > mm/rmap.c | 5 +-
> > mm/swap.c | 6 +-
> > mm/swap_state.c | 8 +-
> > mm/vmstat.c | 5 +-
> > tools/include/uapi/linux/perf_event.h | 1 +
> > tools/perf/util/evsel.c | 1 +
> > tools/perf/util/parse-events.c | 4 +
> > tools/perf/util/parse-events.l | 1 +
> > tools/perf/util/python.c | 1 +
> > 44 files changed, 1161 insertions(+), 211 deletions(-)
> > create mode 100644 include/trace/events/pagefault.h
> >
> > --
> > 2.7.4
> >
> >
>
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