Volume 2, Part 2: MP Coherence and Synchronization
2:521
Although each semaphore operation can be decomposed into a read access followed by
a write access, the Itanium architecture does
not
allow a read request by a semaphore
to be satisfied from a store buffer (or other logically-equivalent structure). As a result,
the outcome r1 = 1, r3 = 1, r2 = 0, and r4 = 0 is not allowed. The reasoning is similar
to that presented in
.
Specifically, by the definition of the Itanium memory ordering semantics,
and
. The relative ordering between operation M1 and operations M2 or M3 is not
constrained. Likewise, the relative ordering between operation M4 and operations M5
and M6.
Now, assume the outcome r1 = 1, r3 = 1, r2 = 0, and r4 = 0. Given that r1 = 1, r3 =
1, and r2 = 0, we observe the following:
This conclusion contradicts the assumed outcome where r4 = 0 and thus the outcome
r1 = 1, r3 = 1, r2 = 0, and r4 = 0 is not allowed. Because M1 and M4 cannot become
locally-visible to M2 and M5 before they become globally-visible to M6 and M3 (as read
accesses from semaphores may not bypass from store buffers or other
logically-equivalent structures), it is not possible to avoid this contradiction.
The Itanium architecture also prohibits local bypass from a semaphore operation to a
local read access from a load or acquire load as shown in the execution in
.
Table 2-12.
Bypassing to a Semaphore Operation
Processor #0
Processor #1
mov
r5 = 2
st.rel
[x] = 1
// M1
xchg
r1 = [x], r5
// M2
ld
r2 = [y]
// M3
mov
r6 = 2
st.rel
[y] = 1
// M4
xchg
r3 = [y], r6
// M5
ld
r4 = [x]
// M6
Outcome:
r1 = 1, r3 = 1, r2 = 0, and r4 = 0 is not allowed
Table 2-13.
Bypassing from a Semaphore Operation
Processor #0
Processor #1
fetchadd.rel
r5 = [x], 1
// M1
ld.acq
r1 = [x]
// M2
ld
r2 = [y]
// M3
fetchadd.rel
r6 = [y], 1
// M4
ld.acq
r3 = [y]
// M5
ld
r4 = [x]
// M6
Outcome:
r1 = 1, r3 = 1, r2 = 0, r4 = 0, r5 = 0, and r6 = 0 is not allowed
M2
M3
M5
M6
r1 = 1
M1
M2
r3 = 1
M4
M5
r2 = 0
M3
M4
M3
M4
M1
M6 because M1
M3
M4
M6
M1
M6
r4 = 2
Содержание ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS VOLUME 3 REV 2.3
Страница 1: ......
Страница 11: ...x Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 12: ...1 1 Intel Itanium Architecture Software Developer s Manual Rev 2 3 Part I Application Architecture Guide ...
Страница 13: ...1 2 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 33: ...1 22 Volume 1 Part 1 Introduction to the Intel Itanium Architecture ...
Страница 57: ...1 46 Volume 1 Part 1 Execution Environment ...
Страница 147: ...1 136 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 149: ...1 138 Volume 1 Part 2 About the Optimization Guide ...
Страница 191: ...1 180 Volume 1 Part 2 Predication Control Flow and Instruction Stream ...
Страница 230: ......
Страница 248: ...236 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 249: ...2 1 Intel Itanium Architecture Software Developer s Manual Rev 2 3 Part I System Architecture Guide ...
Страница 250: ...2 2 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 264: ...2 16 Volume 2 Part 1 Intel Itanium System Environment ...
Страница 380: ...2 132 Volume 2 Part 1 Interruptions ...
Страница 398: ...2 150 Volume 2 Part 1 Register Stack Engine ...
Страница 486: ...2 238 Volume 2 Part 1 IA 32 Interruption Vector Descriptions ...
Страница 749: ...2 501 Intel Itanium Architecture Software Developer s Manual Rev 2 3 Part II System Programmer s Guide ...
Страница 750: ...2 502 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 754: ...2 506 Volume 2 Part 2 About the System Programmer s Guide ...
Страница 796: ...2 548 Volume 2 Part 2 Interruptions and Serialization ...
Страница 808: ...2 560 Volume 2 Part 2 Context Management ...
Страница 842: ...2 594 Volume 2 Part 2 Floating point System Software ...
Страница 850: ...2 602 Volume 2 Part 2 IA 32 Application Support ...
Страница 862: ...2 614 Volume 2 Part 2 External Interrupt Architecture ...
Страница 870: ...2 622 Volume 2 Part 2 Performance Monitoring Support ...
Страница 891: ......
Страница 941: ...3 42 Volume 3 Instruction Reference cmp illegal_operation_fault PR p1 0 PR p2 0 Interruptions Illegal Operation fault ...
Страница 1099: ...3 200 Volume 3 Instruction Reference padd Interruptions Illegal Operation fault ...
Страница 1191: ...3 292 Volume 3 Pseudo Code Functions Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 1295: ...3 396 Volume 3 Resource and Dependency Semantics ...
Страница 1296: ......
Страница 1302: ...402 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 1494: ...4 192 Volume 4 Base IA 32 Instruction Reference FWAIT Wait See entry for WAIT ...
Страница 1564: ...4 262 Volume 4 Base IA 32 Instruction Reference LES Load Full Pointer See entry for LDS LES LFS LGS LSS ...
Страница 1565: ...Volume 4 Base IA 32 Instruction Reference 4 263 LFS Load Full Pointer See entry for LDS LES LFS LGS LSS ...
Страница 1568: ...4 266 Volume 4 Base IA 32 Instruction Reference LGS Load Full Pointer See entry for LDS LES LFS LGS LSS ...
Страница 1583: ...Volume 4 Base IA 32 Instruction Reference 4 281 LSS Load Full Pointer See entry for LDS LES LFS LGS LSS ...
Страница 1647: ...Volume 4 Base IA 32 Instruction Reference 4 345 ROL ROR Rotate See entry for RCL RCR ROL ROR ...
Страница 1663: ...Volume 4 Base IA 32 Instruction Reference 4 361 SHL SHR Shift Instructions See entry for SAL SAR SHL SHR ...
Страница 1668: ...4 366 Volume 4 Base IA 32 Instruction Reference SIDT Store Interrupt Descriptor Table Register See entry for SGDT SIDT ...
Страница 1884: ...4 582 Volume 4 IA 32 SSE Instruction Reference ...
Страница 1885: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 Index ...
Страница 1886: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 1898: ...INDEX Index 12 Index for Volumes 1 2 3 and 4 ...