[Xen-devel] [PATCH v4 0/9] x86/tlb: Concurrent TLB flushes

[Nadav Amit <namit@xxxxxxxxxx>]

[ Similar cover-letter to v3 with updated performance numbers on skylake.
  Sorry for the time it since the last version. ]

Currently, local and remote TLB flushes are not performed concurrently,
which introduces unnecessary overhead - each PTE flushing can take 100s
of cycles. This patch-set allows TLB flushes to be run concurrently:
first request the remote CPUs to initiate the flush, then run it
locally, and finally wait for the remote CPUs to finish their work.

In addition, there are various small optimizations to avoid, for
example, unwarranted false-sharing.

The proposed changes should also improve the performance of other
invocations of on_each_cpu(). Hopefully, no one has relied on this
behavior of on_each_cpu() that invoked functions first remotely and only
then locally [Peter says he remembers someone might do so, but without
further information it is hard to know how to address it].

Running sysbench on dax/ext4 w/emulated-pmem, write-cache disabled on
2-socket, 56-logical-cores (28+SMT) Skylake, 5 repetitions:

sysbench fileio --file-total-size=3G --file-test-mode=rndwr \
 --file-io-mode=mmap --threads=X --file-fsync-mode=fdatasync run

 Th.   tip-aug22 avg (stdev)   +patch-set avg (stdev)  change
 ---   ---------------------   ----------------------  ------
 1      1152920 (7453)          1169469 (9059)          +1.4%
 2      1545832 (12555)         1584172 (10484)         +2.4%
 4      2480703 (12039)         2518641 (12875)         +1.5%
 8      3684486 (26007)         3840343 (44144)         +4.2%
 16     4981567 (23565)         5125756 (15458)         +2.8%
 32     5679542 (10116)         5887826 (6121)          +3.6%
 56     5630944 (17937)         5812514 (26264)         +3.2%

(Note that on configurations with up to 28 threads numactl was used to
set all threads on socket 1, which explains the drop in performance when
going to 32 threads).

Running the same benchmark with security mitigations disabled (PTI,
Spectre, MDS):

 Th.   tip-aug22 avg (stdev)   +patch-set avg (stdev)  change
 ---   ---------------------   ----------------------  ------
 1      1444119 (8524)          1469606 (10527)         +1.7%
 2      1921540 (24169)         1961899 (14450)         +2.1%
 4      3073716 (21786)         3199880 (16774)         +4.1%
 8      4700698 (49534)         4802312 (11043)         +2.1%
 16     6005180 (6366)          6006656 (31624)            0%
 32     6826466 (10496)         6886622 (19110)         +0.8%
 56     6832344 (13468)         6885586 (20646)         +0.8%

The results are somewhat different than the results that have been obtained on
Haswell-X, which were sent before and the maximum performance improvement is
smaller. However, the performance improvement is significant.

v3 -> v4:
  * Merge flush_tlb_func_local and flush_tlb_func_remote() [Peter]
  * Prevent preemption on_each_cpu(). It is not needed, but it prevents
    concerns. [Peter/tglx]
  * Adding acked-, review-by tags

v2 -> v3:
* Open-code the remote/local-flush decision code [Andy]
* Fix hyper-v, Xen implementations [Andrew]
* Fix redundant TLB flushes.

v1 -> v2:
* Removing the patches that Thomas took [tglx]
* Adding hyper-v, Xen compile-tested implementations [Dave]
* Removing UV [Andy]
* Adding lazy optimization, removing inline keyword [Dave]
* Restructuring patch-set

RFCv2 -> v1:
* Fix comment on flush_tlb_multi [Juergen]
* Removing async invalidation optimizations [Andy]
* Adding KVM support [Paolo]

Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Sasha Levin <sashal@xxxxxxxxxx>
Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: kvm@xxxxxxxxxxxxxxx
Cc: linux-hyperv@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
Cc: x86@xxxxxxxxxx
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx

Nadav Amit (9):
  smp: Run functions concurrently in smp_call_function_many()
  x86/mm/tlb: Unify flush_tlb_func_local() and flush_tlb_func_remote()
  x86/mm/tlb: Open-code on_each_cpu_cond_mask() for tlb_is_not_lazy()
  x86/mm/tlb: Flush remote and local TLBs concurrently
  x86/mm/tlb: Privatize cpu_tlbstate
  x86/mm/tlb: Do not make is_lazy dirty for no reason
  cpumask: Mark functions as pure
  x86/mm/tlb: Remove UV special case
  x86/mm/tlb: Remove unnecessary uses of the inline keyword

 arch/x86/hyperv/mmu.c                 |  10 +-
 arch/x86/include/asm/paravirt.h       |   6 +-
 arch/x86/include/asm/paravirt_types.h |   4 +-
 arch/x86/include/asm/tlbflush.h       |  52 +++----
 arch/x86/include/asm/trace/hyperv.h   |   2 +-
 arch/x86/kernel/kvm.c                 |  11 +-
 arch/x86/kernel/paravirt.c            |   2 +-
 arch/x86/mm/init.c                    |   2 +-
 arch/x86/mm/tlb.c                     | 195 ++++++++++++++------------
 arch/x86/xen/mmu_pv.c                 |  11 +-
 include/linux/cpumask.h               |   6 +-
 include/linux/smp.h                   |  34 ++++-
 include/trace/events/xen.h            |   2 +-
 kernel/smp.c                          | 138 +++++++++---------
 14 files changed, 254 insertions(+), 221 deletions(-)

-- 
2.17.1


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