Commit Graph

1692 Commits

Author SHA1 Message Date
Alistair Francis
6cd2eda39f tcg/riscv: Add the mov and movi instruction
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Michael Clark <mjc@sifive.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <bd6a45c73a67b77ddaa2fe590a6bb8ee422b9683.1545246859.git.alistair.francis@wdc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-26 06:40:02 +11:00
Alistair Francis
dfa8e74f94 tcg/riscv: Add the relocation functions
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Michael Clark <mjc@sifive.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <6ac4f4b0d5ea93cb0ee9a3b8b47ee9f7b3711494.1545246859.git.alistair.francis@wdc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-26 06:40:02 +11:00
Alistair Francis
bedf14e335 tcg/riscv: Add the instruction emitters
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Michael Clark <mjc@sifive.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <c740aca183675625bb9cf3ce7b9e8b9d431ca694.1545246859.git.alistair.francis@wdc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-26 06:40:02 +11:00
Alistair Francis
54a9ce0f68 tcg/riscv: Add the immediate encoders
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Michael Clark <mjc@sifive.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <d54dc56303fd1b0d7ed53869de2dbb59b111c7ca.1545246859.git.alistair.francis@wdc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-26 06:40:02 +11:00
Alistair Francis
8ce23a1312 tcg/riscv: Add support for the constraints
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Michael Clark <mjc@sifive.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <dba7315e4e20e879933f72d47ccf98f1cc612b8a.1545246859.git.alistair.francis@wdc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-26 06:40:02 +11:00
Alistair Francis
505e75c592 tcg/riscv: Add the tcg target registers
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Michael Clark <mjc@sifive.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <6e43abaa64361d57b9bc9439820d0e7701f2d47e.1545246859.git.alistair.francis@wdc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-26 06:40:02 +11:00
Alistair Francis
fb1f70f368 tcg/riscv: Add the tcg-target.h file
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Michael Clark <mjc@sifive.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <a135ee1a88cd7bd08993a519d4d654da27785254.1545246859.git.alistair.francis@wdc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-26 06:40:02 +11:00
Emilio G. Cota
ac1043f6d6 tcg: Drop nargs from tcg_op_insert_{before,after}
It's unused since 75e8b9b7aa.

Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <20181209193749.12277-9-cota@braap.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:44 +03:00
Alistair Francis
161dec9d1b tcg/mips: Improve the add2/sub2 command to use TCG_TARGET_REG_BITS
Instead of hard coding 31 for the shift right use TCG_TARGET_REG_BITS - 1.

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <7dfbddf7014a595150aa79011ddb342c3cc17ec3.1544648105.git.alistair.francis@wdc.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:44 +03:00
Richard Henderson
e1dcf3529d tcg: Add TCG_TARGET_HAS_MEMORY_BSWAP
For now, defined universally as true, since we previously required
backends to implement swapped memory operations.  Future patches
may now remove that support where it is onerous.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:44 +03:00
Richard Henderson
6498594c8e tcg/optimize: Optimize bswap
Somehow we forgot these operations, once upon a time.
This will allow immediate stores to have their bswap
optimized away.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:44 +03:00
Richard Henderson
9e821eab0a tcg: Clean up generic bswap64
Based on the only current user, Sparc:

New code uses 2 constants that take 2 insns to load from constant pool,
plus 13.  Old code used 6 constants that took 1 or 2 insns to create,
plus 21.  The result is a new total of 17 vs an old total of 29.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:44 +03:00
Richard Henderson
a686dc71d8 tcg: Clean up generic bswap32
Based on the only current user, Sparc:

New code uses 1 constant that takes 2 insns to create, plus 8.
Old code used 2 constants that took 2 insns to create, plus 9.
The result is a new total of 10 vs an old total of 13.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:44 +03:00
Richard Henderson
5785c17f31 tcg/i386: Add setup_guest_base_seg for FreeBSD
Reviewed-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:44 +03:00
Richard Henderson
913c2bddc2 tcg/i386: Precompute all guest_base parameters
These values are constant between all qemu_ld/st invocations;
there is no need to figure this out each time.  If we cannot
use a segment or an offset directly for guest_base, load the
value into a register in the prologue.

Reviewed-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:44 +03:00
Richard Henderson
4810d96f03 tcg/i386: Assume 32-bit values are zero-extended
We now have an invariant that all TCG_TYPE_I32 values are
zero-extended, which means that we do not need to extend
them again during qemu_ld/st, either explicitly via a separate
tcg_out_ext32u or implicitly via P_ADDR32.

Reviewed-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:44 +03:00
Richard Henderson
75478279a0 tcg/i386: Implement INDEX_op_extr{lh}_i64_i32 for 32-bit guests
This preserves the invariant that all TCG_TYPE_I32 values are
zero-extended in the 64-bit host register.

Reviewed-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:44 +03:00
Richard Henderson
3dbc8c61de tcg/i386: Propagate is64 to tcg_out_qemu_ld_slow_path
This helps preserve the invariant that all TCG_TYPE_I32 values
are stored zero-extended in the 64-bit host registers.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:44 +03:00
Richard Henderson
1d21d95b61 tcg/i386: Propagate is64 to tcg_out_qemu_ld_direct
This helps preserve the invariant that all TCG_TYPE_I32 values
are stored zero-extended in the 64-bit host registers.

Reviewed-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:43 +03:00
Richard Henderson
55dfd8fedc tcg/s390x: Return false on failure from patch_reloc
This does require an extra two checks within the slow paths
to replace the assert that we're moving.  Also add two checks
within existing functions that lacked any kind of assert for
out of range branch.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:43 +03:00
Richard Henderson
d513290351 tcg/ppc: Return false on failure from patch_reloc
The reloc_pc{14,24}_val routines retain their asserts.
Use these directly within the slow paths.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:43 +03:00
Richard Henderson
43fabd30e2 tcg/arm: Return false on failure from patch_reloc
This does require an extra two checks within the slow paths
to replace the assert that we're moving.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:43 +03:00
Richard Henderson
214bfe83d5 tcg/aarch64: Return false on failure from patch_reloc
This does require an extra two checks within the slow paths
to replace the assert that we're moving.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:43 +03:00
Richard Henderson
bec3afd5fc tcg/i386: Return false on failure from patch_reloc
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:43 +03:00
Richard Henderson
6ac1778676 tcg: Return success from patch_reloc
This will move the assert for success from within (subroutines of)
patch_reloc into the callers.  It will also let new code do something
different when a relocation is out of range.

For the moment, all backends are trivially converted to return true.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:43 +03:00
Richard Henderson
8c1b079279 tcg/mips: Remove retranslation code
There is no longer a need for preserving branch offset operands,
as we no longer re-translate.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:43 +03:00
Richard Henderson
791645f022 tcg/sparc: Remove retranslation code
There is no longer a need for preserving branch offset operands,
as we no longer re-translate.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:43 +03:00
Richard Henderson
3661612fc3 tcg/s390: Remove retranslation code
There is no longer a need for preserving branch offset operands,
as we no longer re-translate.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:43 +03:00
Richard Henderson
f9c7246faa tcg/ppc: Fold away "noaddr" branch routines
There is no longer a need for preserving branch offset operands,
as we no longer re-translate.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:43 +03:00
Richard Henderson
37ee93a974 tcg/arm: Fold away "noaddr" branch routines
There are one use apiece for these.  There is no longer a need for
preserving branch offset operands, as we no longer re-translate.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:43 +03:00
Richard Henderson
2672ccc7ee tcg/arm: Remove reloc_pc24_atomic
It is unused since 3fb53fb4d1.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:43 +03:00
Richard Henderson
733589b338 tcg/aarch64: Fold away "noaddr" branch routines
There are one use apiece for these.  There is no longer a need for
preserving branch offset operands, as we no longer re-translate.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:43 +03:00
Richard Henderson
90d6cb7811 tcg/aarch64: Remove reloc_pc26_atomic
It is unused since b68686bd4b.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:43 +03:00
Richard Henderson
66c0285df4 tcg/i386: Move TCG_REG_CALL_STACK from define to enum
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:43 +03:00
Richard Henderson
5740d9f714 tcg/i386: Always use %ebp for TCG_AREG0
For x86_64, this can remove a REX prefix resulting in smaller code
when manipulating globals of type i32, as we move them between backing
store via cpu_env, aka TCG_AREG0.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:43 +03:00
Richard Henderson
f6823cbe37 target/sparc: Remove the constant pool
Partially reverts ab20bdc116.  The 14-bit displacement that we
allowed to reach the constant pool is not always sufficient.
Retain the tb-relative addressing, as that is how most return
values from the tb are computed.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:42 +03:00
Thomas Huth
6fa2cef205 tcg/tcg.h: Remove GCC check for tcg_debug_assert() macro
Both GCC v4.8 and Clang v3.4 (our minimum versions) support
__builtin_unreachable(), so we can remove the version check here now.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>
2018-12-12 10:01:12 +01:00
Peter Maydell
a7ce790a02 tcg/tcg-op.h: Add multiple include guard
The tcg-op.h header was missing the usual guard against multiple
inclusion; add it.

(Spotted by lgtm.com's static analyzer.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20181108125256.30986-1-peter.maydell@linaro.org
2018-11-08 15:15:32 +00:00
Richard Henderson
e6cd4bb59b tcg: Split CONFIG_ATOMIC128
GCC7+ will no longer advertise support for 16-byte __atomic operations
if only cmpxchg is supported, as for x86_64.  Fortunately, x86_64 still
has support for __sync_compare_and_swap_16 and we can make use of that.
AArch64 does not have, nor ever has had such support, so open-code it.

Reviewed-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-10-18 19:46:36 -07:00
Emilio G. Cota
72fd2efbbd tcg: distribute tcg_time into TCG contexts
When we implemented per-vCPU TCG contexts, we forgot to also
distribute the tcg_time counter, which has remained as a global
accessed without any serialization, leading to potentially missed
counts.

Fix it by distributing the field over the TCG contexts, embedding
it into TCGProfile with a field called "cpu_exec_time", which is more
descriptive than "tcg_time". Add a function to query this value
directly, and for completeness, fill in the field in
tcg_profile_snapshot, even though its callers do not use it.

Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <20181010144853.13005-5-cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-10-18 18:58:10 -07:00
Emilio G. Cota
dd1d7da23b tcg: plug holes in struct TCGProfile
This plugs two 4-byte holes in 64-bit.

Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <20181010144853.13005-4-cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-10-18 18:58:10 -07:00
Emilio G. Cota
c1f543b739 tcg: fix use of uninitialized variable under CONFIG_PROFILER
We forgot to initialize n in commit 15fa08f845 ("tcg: Dynamically
allocate TCGOps", 2017-12-29).

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <20181010144853.13005-3-cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-10-18 18:58:10 -07:00
Richard Henderson
d7f425fdea tcg: Implement CPU_LOG_TB_NOCHAIN during expansion
Rather than test NOCHAIN before linking, do not emit the
goto_tb opcode at all.  We already do this for goto_ptr.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-10-18 18:58:10 -07:00
Roman Kapl
93bf9a4273 tcg/i386: fix vector operations on 32-bit hosts
The TCG backend uses LOWREGMASK to get the low 3 bits of register numbers.
This was defined as no-op for 32-bit x86, with the assumption that we have
eight registers anyway. This assumption is not true once we have xmm regs.

Since LOWREGMASK was a no-op, xmm register indidices were wrong in opcodes
and have overflown into other opcode fields, wreaking havoc.

To trigger these problems, you can try running the "movi d8, #0x0" AArch64
instruction on 32-bit x86. "vpxor %xmm0, %xmm0, %xmm0" should be generated,
but instead TCG generated "vpxor %xmm0, %xmm0, %xmm2".

Fixes: 770c2fc7bb ("Add vector operations")
Signed-off-by: Roman Kapl <rka@sysgo.com>
Message-Id: <20180824131734.18557-1-rka@sysgo.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-09-26 09:02:51 -07:00
Richard Henderson
1fb57da72a tcg/optimize: Do not skip default processing of dup_vec
If we do not opimize away dup_vec, we must mark its output as changed.

Fixes: 170ba88f45
Reported-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Tested-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Message-id: 20180805233258.31892-1-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
2018-08-06 14:57:48 +01:00
Richard Henderson
672189cd58 tcg/i386: Mark xmm registers call-clobbered
When host vector registers and operations were introduced, I failed
to mark the registers call clobbered as required by the ABI.

Fixes: 770c2fc7bb
Cc: qemu-stable@nongnu.org
Reported-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-07-23 09:21:14 -07:00
Alex Bennée
e65a5f227d tcg/aarch64: limit mul_vec size
In AdvSIMD we can only do 32x32 integer multiples although SVE is
capable of larger 64 bit multiples. As a result we can end up
generating invalid opcodes. Fix this by only reprting we can emit
mul vector ops if the size is small enough.

Fixes a crash on:

  sve-all-short-v8.3+sve@vq3/insn_mul_z_zi___INC.risu.bin

When running on AArch64 hardware.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20180719154248.29669-1-alex.bennee@linaro.org>
[rth: Removed the tcg_debug_assert -- there are plenty of other
cases that we do not diagnose within the insn encoding helpers.]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-07-19 09:07:31 -07:00
Richard Henderson
499748d768 tcg: Restrict check_size_impl to multiples of the line size
Normally this is automatic in the size restrictions that are placed
on vector sizes coming from the implementation.  However, for the
legitimate size tuple [oprsz=8, maxsz=32], we need to clear the final
24 bytes of the vector register.  Without this check, do_dup selects
TCG_TYPE_V128 and clears only 16 bytes.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20180705191929.30773-2-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
2018-07-09 14:51:34 +01:00
Richard Henderson
9f75462065 tcg: Reduce max TB opcode count
Also, assert that we don't overflow any of two different offsets into
the TB. Both unwind and goto_tb both record a uint16_t for later use.

This fixes an arm-softmmu test case utilizing NEON in which there is
a TB generated that runs to 7800 opcodes, and compiles to 96k on an
x86_64 host.  This overflows the 16-bit offset in which we record the
goto_tb reset offset.  Because of that overflow, we install a jump
destination that goes to neverland.  Boom.

With this reduced op count, the same TB compiles to about 48k for
aarch64, ppc64le, and x86_64 hosts, and neither assertion fires.

Cc: qemu-stable@nongnu.org
Reported-by: "Jason A. Donenfeld" <Jason@zx2c4.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-06-15 09:39:53 -10:00
Emilio G. Cota
0ac20318ce tcg: remove tb_lock
Use mmap_lock in user-mode to protect TCG state and the page descriptors.
In !user-mode, each vCPU has its own TCG state, so no locks needed.
Per-page locks are used to protect the page descriptors.

Per-TB locks are used in both modes to protect TB jumps.

Some notes:

- tb_lock is removed from notdirty_mem_write by passing a
  locked page_collection to tb_invalidate_phys_page_fast.

- tcg_tb_lookup/remove/insert/etc have their own internal lock(s),
  so there is no need to further serialize access to them.

- do_tb_flush is run in a safe async context, meaning no other
  vCPU threads are running. Therefore acquiring mmap_lock there
  is just to please tools such as thread sanitizer.

- Not visible in the diff, but tb_invalidate_phys_page already
  has an assert_memory_lock.

- cpu_io_recompile is !user-only, so no mmap_lock there.

- Added mmap_unlock()'s before all siglongjmp's that could
  be called in user-mode while mmap_lock is held.
  + Added an assert for !have_mmap_lock() after returning from
    the longjmp in cpu_exec, just like we do in cpu_exec_step_atomic.

Performance numbers before/after:

Host: AMD Opteron(tm) Processor 6376

                 ubuntu 17.04 ppc64 bootup+shutdown time

  700 +-+--+----+------+------------+-----------+------------*--+-+
      |    +    +      +            +           +           *B    |
      |         before ***B***                            ** *    |
      |tb lock removal ###D###                         ***        |
  600 +-+                                           ***         +-+
      |                                           **         #    |
      |                                        *B*          #D    |
      |                                     *** *         ##      |
  500 +-+                                ***           ###      +-+
      |                             * ***           ###           |
      |                            *B*          # ##              |
      |                          ** *          #D#                |
  400 +-+                      **            ##                 +-+
      |                      **           ###                     |
      |                    **           ##                        |
      |                  **         # ##                          |
  300 +-+  *           B*          #D#                          +-+
      |    B         ***        ###                               |
      |    *       **       ####                                  |
      |     *   ***      ###                                      |
  200 +-+   B  *B     #D#                                       +-+
      |     #B* *   ## #                                          |
      |     #*    ##                                              |
      |    + D##D#     +            +           +            +    |
  100 +-+--+----+------+------------+-----------+------------+--+-+
           1    8      16      Guest CPUs       48           64
  png: https://imgur.com/HwmBHXe

              debian jessie aarch64 bootup+shutdown time

  90 +-+--+-----+-----+------------+------------+------------+--+-+
     |    +     +     +            +            +            +    |
     |         before ***B***                                B    |
  80 +tb lock removal ###D###                              **D  +-+
     |                                                   **###    |
     |                                                 **##       |
  70 +-+                                             ** #       +-+
     |                                             ** ##          |
     |                                           **  #            |
  60 +-+                                       *B  ##           +-+
     |                                       **  ##               |
     |                                    ***  #D                 |
  50 +-+                               ***   ##                 +-+
     |                             * **   ###                     |
     |                           **B*  ###                        |
  40 +-+                     ****  # ##                         +-+
     |                   ****     #D#                             |
     |             ***B**      ###                                |
  30 +-+    B***B**        ####                                 +-+
     |    B *   *     # ###                                       |
     |     B       ###D#                                          |
  20 +-+   D  ##D##                                             +-+
     |      D#                                                    |
     |    +     +     +            +            +            +    |
  10 +-+--+-----+-----+------------+------------+------------+--+-+
          1     8     16      Guest CPUs        48           64
  png: https://imgur.com/iGpGFtv

The gains are high for 4-8 CPUs. Beyond that point, however, unrelated
lock contention significantly hurts scalability.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-06-15 08:18:48 -10:00