diff options
| -rw-r--r-- | Documentation/cpu-hotplug.txt | 32 | ||||
| -rw-r--r-- | Documentation/ko_KR/memory-barriers.txt | 36 |
2 files changed, 52 insertions, 16 deletions
diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt index dd68821c22d4..d02e8a451872 100644 --- a/Documentation/cpu-hotplug.txt +++ b/Documentation/cpu-hotplug.txt @@ -84,9 +84,9 @@ are added or removed anytime. Trimming it accurately for your system needs upfront can save some boot time memory. See below for how we use heuristics in x86_64 case to keep this under check. -cpu_online_mask: Bitmap of all CPUs currently online. Its set in __cpu_up() -after a cpu is available for kernel scheduling and ready to receive -interrupts from devices. Its cleared when a cpu is brought down using +cpu_online_mask: Bitmap of all CPUs currently online. It's set in __cpu_up() +after a CPU is available for kernel scheduling and ready to receive +interrupts from devices. It's cleared when a CPU is brought down using __cpu_disable(), before which all OS services including interrupts are migrated to another target CPU. @@ -181,7 +181,7 @@ To support physical addition/removal, one would need some BIOS hooks and the platform should have something like an attention button in PCI hotplug. CONFIG_ACPI_HOTPLUG_CPU enables ACPI support for physical add/remove of CPUs. -Q: How do i logically offline a CPU? +Q: How do I logically offline a CPU? A: Do the following. #echo 0 > /sys/devices/system/cpu/cpuX/online @@ -191,15 +191,15 @@ Once the logical offline is successful, check #cat /proc/interrupts You should now not see the CPU that you removed. Also online file will report -the state as 0 when a cpu if offline and 1 when its online. +the state as 0 when a CPU is offline and 1 when it's online. #To display the current cpu state. #cat /sys/devices/system/cpu/cpuX/online -Q: Why can't i remove CPU0 on some systems? +Q: Why can't I remove CPU0 on some systems? A: Some architectures may have some special dependency on a certain CPU. -For e.g in IA64 platforms we have ability to sent platform interrupts to the +For e.g in IA64 platforms we have ability to send platform interrupts to the OS. a.k.a Corrected Platform Error Interrupts (CPEI). In current ACPI specifications, we didn't have a way to change the target CPU. Hence if the current ACPI version doesn't support such re-direction, we disable that CPU @@ -231,7 +231,7 @@ either by CONFIG_BOOTPARAM_HOTPLUG_CPU0 or by kernel parameter cpu0_hotplug. --Fenghua Yu <[email protected]> -Q: How do i find out if a particular CPU is not removable? +Q: How do I find out if a particular CPU is not removable? A: Depending on the implementation, some architectures may show this by the absence of the "online" file. This is done if it can be determined ahead of time that this CPU cannot be removed. @@ -250,7 +250,7 @@ A: The following happen, listed in no particular order :-) - All processes are migrated away from this outgoing CPU to new CPUs. The new CPU is chosen from each process' current cpuset, which may be a subset of all online CPUs. -- All interrupts targeted to this CPU is migrated to a new CPU +- All interrupts targeted to this CPU are migrated to a new CPU - timers/bottom half/task lets are also migrated to a new CPU - Once all services are migrated, kernel calls an arch specific routine __cpu_disable() to perform arch specific cleanup. @@ -259,10 +259,10 @@ A: The following happen, listed in no particular order :-) CPU is being offlined). "It is expected that each service cleans up when the CPU_DOWN_PREPARE - notifier is called, when CPU_DEAD is called its expected there is nothing + notifier is called, when CPU_DEAD is called it's expected there is nothing running on behalf of this CPU that was offlined" -Q: If i have some kernel code that needs to be aware of CPU arrival and +Q: If I have some kernel code that needs to be aware of CPU arrival and departure, how to i arrange for proper notification? A: This is what you would need in your kernel code to receive notifications. @@ -311,7 +311,7 @@ things will happen if a notifier in path sent a BAD notify code. Q: I don't see my action being called for all CPUs already up and running? A: Yes, CPU notifiers are called only when new CPUs are on-lined or offlined. - If you need to perform some action for each cpu already in the system, then + If you need to perform some action for each CPU already in the system, then do this: for_each_online_cpu(i) { @@ -363,8 +363,8 @@ A: Yes, CPU notifiers are called only when new CPUs are on-lined or offlined. callbacks as well as initialize the already online CPUs. -Q: If i would like to develop cpu hotplug support for a new architecture, - what do i need at a minimum? +Q: If I would like to develop CPU hotplug support for a new architecture, + what do I need at a minimum? A: The following are what is required for CPU hotplug infrastructure to work correctly. @@ -382,8 +382,8 @@ A: The following are what is required for CPU hotplug infrastructure to work per_cpu state to be set, to ensure the processor dead routine is called to be sure positively. -Q: I need to ensure that a particular cpu is not removed when there is some - work specific to this cpu is in progress. +Q: I need to ensure that a particular CPU is not removed when there is some + work specific to this CPU in progress. A: There are two ways. If your code can be run in interrupt context, use smp_call_function_single(), otherwise use work_on_cpu(). Note that work_on_cpu() is slow, and can fail due to out of memory: diff --git a/Documentation/ko_KR/memory-barriers.txt b/Documentation/ko_KR/memory-barriers.txt index 34d3d380893d..a3228a676cc1 100644 --- a/Documentation/ko_KR/memory-barriers.txt +++ b/Documentation/ko_KR/memory-barriers.txt @@ -823,6 +823,38 @@ CPU 는 b 로부터의 로드 오퍼레이션이 a 로부터의 로드 오퍼레 오퍼레이션을 위한 코드를 정말로 만들도록 하지만, 컴파일러가 그렇게 만들어진 코드의 수행 결과를 사용하도록 강제하지는 않습니다. +또한, 컨트롤 의존성은 if 문의 then 절과 else 절에 대해서만 적용됩니다. 상세히 +말해서, 컨트롤 의존성은 if 문을 뒤따르는 코드에는 적용되지 않습니다: + + q = READ_ONCE(a); + if (q) { + WRITE_ONCE(b, p); + } else { + WRITE_ONCE(b, r); + } + WRITE_ONCE(c, 1); /* BUG: No ordering against the read from "a". */ + +컴파일러는 volatile 타입에 대한 액세스를 재배치 할 수 없고 이 조건 하의 "b" +로의 쓰기를 재배치 할 수 없기 때문에 여기에 순서 규칙이 존재한다고 주장하고 +싶을 겁니다. 불행히도 이 경우에, 컴파일러는 다음의 가상의 pseudo-assembly 언어 +코드처럼 "b" 로의 두개의 쓰기 오퍼레이션을 conditional-move 인스트럭션으로 +번역할 수 있습니다: + + ld r1,a + ld r2,p + ld r3,r + cmp r1,$0 + cmov,ne r4,r2 + cmov,eq r4,r3 + st r4,b + st $1,c + +완화된 순서 규칙의 CPU 는 "a" 로부터의 로드와 "c" 로의 스토어 사이에 어떤 +종류의 의존성도 갖지 않을 겁니다. 이 컨트롤 의존성은 두개의 cmov 인스트럭션과 +거기에 의존하는 스토어 에게만 적용될 겁니다. 짧게 말하자면, 컨트롤 의존성은 +주어진 if 문의 then 절과 else 절에게만 (그리고 이 두 절 내에서 호출되는 +함수들에게까지) 적용되지, 이 if 문을 뒤따르는 코드에는 적용되지 않습니다. + 마지막으로, 컨트롤 의존성은 이행성 (transitivity) 을 제공하지 -않습니다-. 이건 x 와 y 가 둘 다 0 이라는 초기값을 가졌다는 가정 하의 두개의 예제로 보이겠습니다: @@ -883,6 +915,10 @@ http://www.cl.cam.ac.uk/users/pes20/ppc-supplemental/test6.pdf 와 의존성이 사라지지 않게 하는데 도움을 줄 수 있습니다. 더 많은 정보를 위해선 "컴파일러 배리어" 섹션을 참고하시기 바랍니다. + (*) 컨트롤 의존성은 컨트롤 의존성을 갖는 if 문의 then 절과 else 절과 이 두 절 + 내에서 호출되는 함수들에만 적용됩니다. 컨트롤 의존성은 컨트롤 의존성을 + 갖는 if 문을 뒤따르는 코드에는 적용되지 -않습니다-. + (*) 컨트롤 의존성은 보통 다른 타입의 배리어들과 짝을 맞춰 사용됩니다. (*) 컨트롤 의존성은 이행성을 제공하지 -않습니다-. 이행성이 필요하다면, |