Re: [PATCH v8 00/10] qspinlock: a 4-byte queue spinlock with PV support

[Konrad Rzeszutek Wilk]

On Wed, Apr 02, 2014 at 10:32:01AM -0400, Konrad Rzeszutek Wilk wrote:
> On Wed, Apr 02, 2014 at 09:27:29AM -0400, Waiman Long wrote:
> > N.B. Sorry for the duplicate. This patch series were resent as the
> >      original one was rejected by the vger.kernel.org list server
> >      due to long header. There is no change in content.
> > 
> > v7->v8:
> >   - Remove one unneeded atomic operation from the slowpath, thus
> >     improving performance.
> >   - Simplify some of the codes and add more comments.
> >   - Test for X86_FEATURE_HYPERVISOR CPU feature bit to enable/disable
> >     unfair lock.
> >   - Reduce unfair lock slowpath lock stealing frequency depending
> >     on its distance from the queue head.
> >   - Add performance data for IvyBridge-EX CPU.
> 
> FYI, your v7 patch with 32 VCPUs (on a 32 cpu socket machine) on an
> HVM guest under Xen after a while stops working. The workload
> is doing 'make -j32' on the Linux kernel.
> 
> Completely unresponsive. Thoughts?

Each VCPU seems to be stuck with this stack trace:

rip: ffffffff810013a8 xen_hypercall_sched_op+0x8
flags: 00000002 nz
rsp: ffff88029f13fb98
rax: 0000000000000000   rcx: 00000000fffffffa   rdx: 0000000000000000
rbx: 0000000000000000   rsi: ffff88029f13fba8   rdi: 0000000000000003
rbp: ffff88029f13fbd0    r8: ffff8807ee65a1c0    r9: ffff88080d800b10
r10: 00000000000048cb   r11: 0000000000000000   r12: 0000000000000013
r13: 0000000000000004   r14: 0000000000000001   r15: ffffea00076a8cd0
 cs: 0010        ss: 0000        ds: 0000        es: 0000
 fs: 0000 @ 00002b24c3e7e380
 gs: 0000 @ ffff88080e200000/0000000000000000
Code (instr addr ffffffff810013a8)
cc cc cc cc cc cc cc cc cc cc cc cc cc b8 1d 00 00 00 0f 01 c1 <c3> cc cc cc cc cc cc cc cc cc cc


Stack:
 ffffffff81352d9e 000000299f13fbb0 ffff88029f13fba4 ffff880200000001
 0000000000000000 ffff88029f13fbd0 0000000000000045 ffff88029f13fbe0
 ffffffff81354240 ffff88029f13fc00 ffffffff81012cb6 ffff88080f4da200
 ffff88080e214b00 ffff88029f13fc48 ffffffff815e4631 0000000000000000

Call Trace:
  [<ffffffff810013a8>] xen_hypercall_sched_op+0x8  <--
  [<ffffffff81352d9e>] xen_poll_irq_timeout+0x3e
  [<ffffffff81354240>] xen_poll_irq+0x10
  [<ffffffff81012cb6>] xen_hibernate+0x46
  [<ffffffff815e4631>] queue_spin_lock_slowerpath+0x84
  [<ffffffff810ab96e>] queue_spin_lock_slowpath+0xee
  [<ffffffff815eff8f>] _raw_spin_lock_irqsave+0x3f
  [<ffffffff81144e4d>] pagevec_lru_move_fn+0x8d
  [<ffffffff81144780>] __pagevec_lru_add_fn
  [<ffffffff81144ed7>] __pagevec_lru_add+0x17
  [<ffffffff81145540>] __lru_cache_add+0x60
  [<ffffffff8114590e>] lru_cache_add+0xe
  [<ffffffff8116d4ba>] page_add_new_anon_rmap+0xda
  [<ffffffff81162ab1>] handle_mm_fault+0xaa1
  [<ffffffff81169d42>] mmap_region+0x2c2
  [<ffffffff815f3c4d>] __do_page_fault+0x18d
  [<ffffffff811544e1>] vm_mmap_pgoff+0xb1
  [<ffffffff815f3fdb>] do_page_fault+0x2b
  [<ffffffff815f06c8>] page_fault+0x28
rip: ffffffff810013a8 xen_hypercall_sched_op+0x8


> 
> (CC ing Marcos who had run the test)
> > 
> > v6->v7:
> >   - Remove an atomic operation from the 2-task contending code
> >   - Shorten the names of some macros
> >   - Make the queue waiter to attempt to steal lock when unfair lock is
> >     enabled.
> >   - Remove lock holder kick from the PV code and fix a race condition
> >   - Run the unfair lock & PV code on overcommitted KVM guests to collect
> >     performance data.
> > 
> > v5->v6:
> >  - Change the optimized 2-task contending code to make it fairer at the
> >    expense of a bit of performance.
> >  - Add a patch to support unfair queue spinlock for Xen.
> >  - Modify the PV qspinlock code to follow what was done in the PV
> >    ticketlock.
> >  - Add performance data for the unfair lock as well as the PV
> >    support code.
> > 
> > v4->v5:
> >  - Move the optimized 2-task contending code to the generic file to
> >    enable more architectures to use it without code duplication.
> >  - Address some of the style-related comments by PeterZ.
> >  - Allow the use of unfair queue spinlock in a real para-virtualized
> >    execution environment.
> >  - Add para-virtualization support to the qspinlock code by ensuring
> >    that the lock holder and queue head stay alive as much as possible.
> > 
> > v3->v4:
> >  - Remove debugging code and fix a configuration error
> >  - Simplify the qspinlock structure and streamline the code to make it
> >    perform a bit better
> >  - Add an x86 version of asm/qspinlock.h for holding x86 specific
> >    optimization.
> >  - Add an optimized x86 code path for 2 contending tasks to improve
> >    low contention performance.
> > 
> > v2->v3:
> >  - Simplify the code by using numerous mode only without an unfair option.
> >  - Use the latest smp_load_acquire()/smp_store_release() barriers.
> >  - Move the queue spinlock code to kernel/locking.
> >  - Make the use of queue spinlock the default for x86-64 without user
> >    configuration.
> >  - Additional performance tuning.
> > 
> > v1->v2:
> >  - Add some more comments to document what the code does.
> >  - Add a numerous CPU mode to support >= 16K CPUs
> >  - Add a configuration option to allow lock stealing which can further
> >    improve performance in many cases.
> >  - Enable wakeup of queue head CPU at unlock time for non-numerous
> >    CPU mode.
> > 
> > This patch set has 3 different sections:
> >  1) Patches 1-4: Introduces a queue-based spinlock implementation that
> >     can replace the default ticket spinlock without increasing the
> >     size of the spinlock data structure. As a result, critical kernel
> >     data structures that embed spinlock won't increase in size and
> >     break data alignments.
> >  2) Patches 5-6: Enables the use of unfair queue spinlock in a
> >     para-virtualized execution environment. This can resolve some
> >     of the locking related performance issues due to the fact that
> >     the next CPU to get the lock may have been scheduled out for a
> >     period of time.
> >  3) Patches 7-10: Enable qspinlock para-virtualization support
> >     by halting the waiting CPUs after spinning for a certain amount of
> >     time. The unlock code will detect the a sleeping waiter and wake it
> >     up. This is essentially the same logic as the PV ticketlock code.
> > 
> > The queue spinlock has slightly better performance than the ticket
> > spinlock in uncontended case. Its performance can be much better
> > with moderate to heavy contention.  This patch has the potential of
> > improving the performance of all the workloads that have moderate to
> > heavy spinlock contention.
> > 
> > The queue spinlock is especially suitable for NUMA machines with at
> > least 2 sockets, though noticeable performance benefit probably won't
> > show up in machines with less than 4 sockets.
> > 
> > The purpose of this patch set is not to solve any particular spinlock
> > contention problems. Those need to be solved by refactoring the code
> > to make more efficient use of the lock or finer granularity ones. The
> > main purpose is to make the lock contention problems more tolerable
> > until someone can spend the time and effort to fix them.
> > 
> > To illustrate the performance benefit of the queue spinlock, the
> > ebizzy benchmark was run with the -m option in two different computers:
> > 
> >   Test machine		ticket-lock		queue-lock
> >   ------------		-----------		----------
> >   4-socket 40-core	2316 rec/s		2899 rec/s
> >   Westmere-EX (HT off)
> >   2-socket 12-core	2130 rec/s		2176 rec/s
> >   Westmere-EP (HT on)
> > 
> > Waiman Long (10):
> >   qspinlock: A generic 4-byte queue spinlock implementation
> >   qspinlock, x86: Enable x86-64 to use queue spinlock
> >   qspinlock: More optimized code for smaller NR_CPUS
> >   qspinlock: Optimized code path for 2 contending tasks
> >   pvqspinlock, x86: Allow unfair spinlock in a PV guest
> >   pvqspinlock: Enable lock stealing in queue lock waiters
> >   pvqspinlock, x86: Rename paravirt_ticketlocks_enabled
> >   pvqspinlock, x86: Add qspinlock para-virtualization support
> >   pvqspinlock, x86: Enable qspinlock PV support for KVM
> >   pvqspinlock, x86: Enable qspinlock PV support for XEN
> > 
> >  arch/x86/Kconfig                      |   12 +
> >  arch/x86/include/asm/paravirt.h       |   17 +-
> >  arch/x86/include/asm/paravirt_types.h |   16 +
> >  arch/x86/include/asm/pvqspinlock.h    |  260 +++++++++
> >  arch/x86/include/asm/qspinlock.h      |  191 +++++++
> >  arch/x86/include/asm/spinlock.h       |    9 +-
> >  arch/x86/include/asm/spinlock_types.h |    4 +
> >  arch/x86/kernel/Makefile              |    1 +
> >  arch/x86/kernel/kvm.c                 |  113 ++++-
> >  arch/x86/kernel/paravirt-spinlocks.c  |   36 ++-
> >  arch/x86/xen/spinlock.c               |  121 ++++-
> >  include/asm-generic/qspinlock.h       |  126 ++++
> >  include/asm-generic/qspinlock_types.h |   63 ++
> >  kernel/Kconfig.locks                  |    7 +
> >  kernel/locking/Makefile               |    1 +
> >  kernel/locking/qspinlock.c            | 1010 +++++++++++++++++++++++++++++++++
> >  16 files changed, 1975 insertions(+), 12 deletions(-)
> >  create mode 100644 arch/x86/include/asm/pvqspinlock.h
> >  create mode 100644 arch/x86/include/asm/qspinlock.h
> >  create mode 100644 include/asm-generic/qspinlock.h
> >  create mode 100644 include/asm-generic/qspinlock_types.h
> >  create mode 100644 kernel/locking/qspinlock.c
> > 
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