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Message-Id: <1374903007.3031.30@driftwood> Date: Sat, 27 Jul 2013 00:30:07 -0500 From: Rob Landley <rob@...dley.net> To: musl@...ts.openwall.com Cc: musl@...ts.openwall.com Subject: Re: Proposed roadmap to 1.0 On 07/24/2013 02:47:19 PM, Rich Felker wrote: > > So... it's hardwired to 1024 cpus. > > > > I don't think there _is_ a way to make this non-ugly. What actually > > uses this? > > That was my question about the whole affinity system in general. My > view is that it's stupid micro-management of scheduling that should be > done by the kernel, and that if the kernel's not doing a good enough > job of managing which cpu a task runs on, the kernel scheduler should > be fixed rather than adding hacks in apps. There are arguments in favor of it, mostly realtime and userspace power management. That said, the only thing that _needs_ to use this stuff is taskset, and everything else can get called _by_ taskset. Toybox implements taskset doesn't use anything out of libc to do so: syscall wrappers and managing its own data structures. Still, you presumably want to build an unmodified util-linux and busybox. The important thing isn't what glibc does, it's what the man pages say. I often start by implementing what the documentation says, building/running real packages, and then submitting bug reports against the docs. The sched_getaffinity() and sched_setaffinity() syscall wrappers seem obvious, and then the _S versions of the macros. Round each size up to the next sizeof(long) bytes. That's pretty much the "should implement this, push patches upstream to make things use 'em" level. man 3 CPU_SET says: CPU_ALLOC() CPU_FREE() CPU_ALLOC_SIZE() // trivial CPU_ZERO_S() CPU_SET_S() CPU_CLR_S() CPU_ISSET_S() CPU_COUNT_S() CPU_AND_S() CPU_OR_S() CPU_XOR_S() CPU_EQUAL_S() That set isn't _that_ disgusting. CPU_ALLOC_SIZE(size) is just (((((size+7)/8)+3)/4)*4 which makes CPU_ALLOC(size) just be malloc(CPU_ALLOC_SIZE(size)) and CPU_FREE(x) is just free(x), and then CPU_ZERO_S(size, set) becomes memset(set, 0, size)... I've posted the set/isset equations here before, and/or/xor are just a for loop where CPU_AND_S(size, dest, src1, src2) is just "do {unsigned __i = size/4; while (__i) {dest[__i] = src1[__i] && src2[__i]; __i--;} } while (0)" or similar, for CPU_COUNT_S you can just cheat and do a bitwise loop with isset (this ain't performance critical)... If you're bored, you could then make the non-S versions can be macros that call the _S versions with a hardwired CPU_SETSIZE argument, and obviously that's #defined to 1024. But "don't use deprecated interfaces" is also a reasonably response. (If ever there's a reason to NOT define stuff unless you #define GNU_DAMMIT it would be the non-S versions of these macros. #ifdef GNU_BRAIN_DAMAGE...) It's evil, but not _that_ evil... Rob
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