Le 06/06/2019 à 08:51, Haiyan Song a écrit : > Hi Laurent, > > Regression test for v12 patch serials have been run on Intel 2s skylake platform, > some regressions were found by LKP-tools (linux kernel performance). Only tested the > cases that have been run and found regressions on v11 patch serials. > > Get the patch serials from https://github.com/ldu4/linux/tree/spf-v12. > Kernel commit: > base: a297558ad4479e0c9c5c14f3f69fe43113f72d1c (v5.1-rc4-mmotm-2019-04-09-17-51) > head: 02c5a1f984a8061d075cfd74986ac8aa01d81064 (spf-v12) > > Benchmark: will-it-scale > Download link: https://github.com/antonblanchard/will-it-scale/tree/master > Metrics: will-it-scale.per_thread_ops=threads/nr_cpu > test box: lkp-skl-2sp8(nr_cpu=72,memory=192G) > THP: enable / disable > nr_task: 100% > > The following is benchmark results, tested 4 times for every case. > > a). Enable THP > base %stddev change head %stddev > will-it-scale.page_fault3.per_thread_ops 63216 ±3% -16.9% 52537 ±4% > will-it-scale.page_fault2.per_thread_ops 36862 -9.8% 33256 > > b). Disable THP > base %stddev change head %stddev > will-it-scale.page_fault3.per_thread_ops 65111 -18.6% 53023 ±2% > will-it-scale.page_fault2.per_thread_ops 38164 -12.0% 33565 Hi Haiyan, Thanks for running this tests on your systems. I did the same tests on my systems (x86 and PowerPc) and I didn't get the same numbers. My x86 system has lower CPUs but larger memory amount but I don't think this impacts a lot since my numbers are far from yours. x86_64 48CPUs 755G 5.1.0-rc4-mm1 5.1.0-rc4-mm1-spf page_fault2_threads SPF OFF SPF ON THP always 2200902.3 [5%] 2152618.8 -2% [4%] 2136316 -3% [7%] THP never 2185616.5 [6%] 2099274.2 -4% [3%] 2123275.1 -3% [7%] 5.1.0-rc4-mm1 5.1.0-rc4-mm1-spf page_fault3_threads SPF OFF SPF ON THP always 2700078.7 [5%] 2789437.1 +3% [4%] 2944806.8 +12% [3%] THP never 2625756.7 [4%] 2944806.8 +12% [8%] 2876525.5 +10% [4%] PowerPC P8 80CPUs 31G 5.1.0-rc4-mm1 5.1.0-rc4-mm1-spf page_fault2_threads SPF OFF SPF ON THP always 171732 [0%] 170762.8 -1% [0%] 170450.9 -1% [0%] THP never 171808.4 [0%] 170600.3 -1% [0%] 170231.6 -1% [0%] 5.1.0-rc4-mm1 5.1.0-rc4-mm1-spf page_fault3_threads SPF OFF SPF ON THP always 2499.6 [13%] 2624.5 +5% [11%] 2734.5 +9% [3%] THP never 2732.5 [2%] 2791.1 +2% [1%] 2695 -3% [4%] Numbers in bracket are the standard deviation percent. I run each test 10 times and then compute the average and deviation. Please find attached the script I run to get these numbers. This would be nice if you could give it a try on your victim node and share the result. Thanks, Laurent. > Best regards, > Haiyan Song > > On Tue, Apr 16, 2019 at 03:44:51PM +0200, Laurent Dufour wrote: >> This is a port on kernel 5.1 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 of page fault is named speculative >> page fault. If the speculative page fault fails because a concurrency has >> been detected or because underlying PMD or PTE tables are not yet >> allocating, it is failing its processing and a regular 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 protecting the MM RB >> tree with RCU and by using a reference counter on each VMA. When fetching a >> VMA under the RCU protection, the VMA's reference counter is incremented to >> ensure that the VMA will not freed in our back during the SPF >> processing. Once that processing is done the VMA's reference counter is >> decremented. To ensure that a VMA is still present when walking the RB tree >> locklessly, the VMA's reference counter is incremented when that VMA is >> linked in the RB tree. When the VMA is unlinked from the RB tree, its >> reference counter will be decremented at the end of the RCU grace period, >> ensuring it will be available during this time. This means that the VMA >> freeing could be delayed and could delay the file closing for file >> mapping. Since the SPF handler is not able to manage file mapping, file is >> closed synchronously and not during the RCU cleaning. This is safe since >> the page fault handler is aborting if a file pointer is associated to the >> VMA. >> >> Using RCU fixes the overhead seen by Haiyan Song using the will-it-scale >> benchmark [2]. >> >> 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 = find_vma_rcu() >> 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 >> ... >> put_vma(vma) >> } >> >> 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:*' >> >> 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 >> >> It is possible to deactivate the speculative page fault handler by echoing >> 0 in /proc/sys/vm/speculative_page_fault. >> >> This series builds on top of v5.1-rc4-mmotm-2019-04-09-17-51 and is >> functional on x86, PowerPC. I cross built it on arm64 but I was not able to >> test it. >> >> This series is also available on github [4]. >> >> --------------------- >> Real Workload results >> >> Test using a "popular in memory multithreaded database product" on 128cores >> SMT8 Power system are in progress and I will come back with performance >> mesurement as soon as possible. With the previous series we seen up to 30% >> improvements in the number of transaction processed per second, and we hope >> this will be the case with this series too. >> >> ------------------ >> Benchmarks results >> >> Base kernel is v5.1-rc4-mmotm-2019-04-09-17-51 >> SPF is BASE + this series >> >> Kernbench: >> ---------- >> Here are the results on a 48 CPUs X86 system using kernbench on a 5.0 >> kernel (kernel is build 5 times): >> >> Average Half load -j 24 >> Run (std deviation) >> BASE SPF >> Elapsed Time 56.52 (1.39185) 56.256 (1.15106) 0.47% >> User Time 980.018 (2.94734) 984.958 (1.98518) -0.50% >> System Time 130.744 (1.19148) 133.616 (0.873573) -2.20% >> Percent CPU 1965.6 (49.682) 1988.4 (40.035) -1.16% >> Context Switches 29926.6 (272.789) 30472.4 (109.569) -1.82% >> Sleeps 124793 (415.87) 125003 (591.008) -0.17% >> >> Average Optimal load -j 48 >> Run (std deviation) >> BASE SPF >> Elapsed Time 46.354 (0.917949) 45.968 (1.42786) 0.83% >> User Time 1193.42 (224.96) 1196.78 (223.28) -0.28% >> System Time 143.306 (13.2726) 146.177 (13.2659) -2.00% >> Percent CPU 2668.6 (743.157) 2699.9 (753.767) -1.17% >> Context Switches 62268.3 (34097.1) 62721.7 (33999.1) -0.73% >> Sleeps 132556 (8222.99) 132607 (8077.6) -0.04% >> >> During a run on the SPF, perf events were captured: >> Performance counter stats for '../kernbench -M': >> 525,873,132 faults >> 242 spf >> 0 pagefault:spf_vma_changed >> 0 pagefault:spf_vma_noanon >> 441 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 1024 CPUs Power8 VM: >> >> 5.1.0-rc4-mm1+ 5.1.0-rc4-mm1-spf-rcu+ >> Average Half load -j 512 Run (std deviation): >> Elapsed Time 52.52 (0.906697) 52.778 (0.510069) -0.49% >> User Time 3855.43 (76.378) 3890.44 (73.0466) -0.91% >> System Time 1977.24 (182.316) 1974.56 (166.097) 0.14% >> Percent CPU 11111.6 (540.461) 11115.2 (458.907) -0.03% >> Context Switches 83245.6 (3061.44) 83651.8 (1202.31) -0.49% >> Sleeps 613459 (23091.8) 628378 (27485.2) -2.43% >> >> Average Optimal load -j 1024 Run (std deviation): >> Elapsed Time 52.964 (0.572346) 53.132 (0.825694) -0.32% >> User Time 4058.22 (222.034) 4070.2 (201.646) -0.30% >> System Time 2672.81 (759.207) 2712.13 (797.292) -1.47% >> Percent CPU 12756.7 (1786.35) 12806.5 (1858.89) -0.39% >> Context Switches 88818.5 (6772) 87890.6 (5567.72) 1.04% >> Sleeps 618658 (20842.2) 636297 (25044) -2.85% >> >> During a run on the SPF, perf events were captured: >> Performance counter stats for '../kernbench -M': >> 149 375 832 faults >> 1 spf >> 0 pagefault:spf_vma_changed >> 0 pagefault:spf_vma_noanon >> 561 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 '. 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 >> 24 CPUs x86 5492.69 9383.07 70.83% >> 1024 CPUS P8 VM 8476.74 17144.38 102% >> >> Here are the performance counter read during a run on a 48 CPUs x86 node: >> Performance counter stats for './ebizzy -mTt 48': >> 11,846,569 faults >> 10,886,706 spf >> 957,702 pagefault:spf_vma_changed >> 0 pagefault:spf_vma_noanon >> 815 pagefault:spf_vma_notsup >> 0 pagefault:spf_vma_access >> 0 pagefault:spf_pmd_changed >> >> And the ones captured during a run on a 1024 CPUs Power VM: >> Performance counter stats for './ebizzy -mTt 1024': >> 1 359 789 faults >> 1 284 910 spf >> 72 085 pagefault:spf_vma_changed >> 0 pagefault:spf_vma_noanon >> 2 669 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 v11 [3] >> - Check vm_ops.fault instead of vm_ops since now all the VMA as a vm_ops. >> - Abort speculative page fault when doing swap readhead because VMA's >> boundaries are not protected at this time. Doing this the first swap in >> is doing a readhead, the next fault should be handled in a speculative >> way as the page is present in the swap read page. >> - Handle a race between copy_pte_range() and the wp_page_copy called by >> the speculative page fault handler. >> - Ported to Kernel v5.0 >> - Moved VM_FAULT_PTNOTSAME define in mm_types.h >> - Use RCU to protect the MM RB tree instead of a rwlock. >> - Add a toggle interface: /proc/sys/vm/speculative_page_fault >> >> [1] https://lore.kernel.org/linux-mm/20141020215633.717315139@infradead.org/ >> [2] https://lore.kernel.org/linux-mm/9FE19350E8A7EE45B64D8D63D368C8966B847F54@SHSMSX101.ccr.corp.intel.com/ >> [3] https://lore.kernel.org/linux-mm/1526555193-7242-1-git-send-email-ldufour@linux.vnet.ibm.com/ >> [4] https://github.com/ldu4/linux/tree/spf-v12 >> >> Laurent Dufour (25): >> 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 against PTE changes done by dup_mmap() >> mm: protect the RB tree with a sequence lock >> mm: introduce vma reference counter >> mm: Introduce find_vma_rcu() >> mm: don't do swap readahead during speculative page fault >> 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 >> mm: Add a speculative page fault switch in sysctl >> >> 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 | 14 + >> fs/exec.c | 1 + >> 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 | 138 +++++- >> include/linux/mm_types.h | 16 +- >> 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 | 35 +- >> kernel/sysctl.c | 9 + >> mm/Kconfig | 22 + >> mm/huge_memory.c | 6 +- >> mm/hugetlb.c | 2 + >> mm/init-mm.c | 3 + >> mm/internal.h | 45 ++ >> mm/khugepaged.c | 5 + >> mm/madvise.c | 6 +- >> mm/memory.c | 631 ++++++++++++++++++++++---- >> mm/mempolicy.c | 51 ++- >> mm/migrate.c | 6 +- >> mm/mlock.c | 13 +- >> mm/mmap.c | 249 ++++++++-- >> mm/mprotect.c | 4 +- >> mm/mremap.c | 13 + >> mm/nommu.c | 1 + >> mm/rmap.c | 5 +- >> mm/swap.c | 6 +- >> mm/swap_state.c | 10 +- >> 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 + >> 45 files changed, 1277 insertions(+), 196 deletions(-) >> create mode 100644 include/trace/events/pagefault.h >> >> -- >> 2.21.0 >>