Date: Thu, 23 Feb 2012 23:43:10 +0100 From: Jilles Tjoelker <jilles@stack.nl> To: davidxu@FreeBSD.org Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org, src-committers@FreeBSD.org Subject: Re: svn commit: r231989 - in head: lib/libthr/thread sys/kern sys/sys Message-ID: <20120223224310.GA10491@stack.nl> In-Reply-To: <4F458355.8090405@gmail.com> References: <201202220322.q1M3MoFE032330@svn.freebsd.org> <20120222234254.GC95122@stack.nl> <4F458355.8090405@gmail.com>
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On Thu, Feb 23, 2012 at 08:07:49AM +0800, David Xu wrote: > On 2012/2/23 7:42, Jilles Tjoelker wrote: > > On Wed, Feb 22, 2012 at 03:22:50AM +0000, David Xu wrote: > >> Author: davidxu > >> Date: Wed Feb 22 03:22:49 2012 > >> New Revision: 231989 > >> URL: http://svn.freebsd.org/changeset/base/231989 > >> Log: > >> Use unused fourth argument of umtx_op to pass flags to kernel for operation > >> UMTX_OP_WAIT. Upper 16bits is enough to hold a clock id, and lower > >> 16bits is used to pass flags. The change saves a clock_gettime() syscall > >> from libthr. > >> Modified: > >> head/lib/libthr/thread/thr_umtx.c > >> head/sys/kern/kern_umtx.c > >> head/sys/sys/umtx.h > >> > >> Modified: head/lib/libthr/thread/thr_umtx.c > >> ============================================================================== > >> --- head/lib/libthr/thread/thr_umtx.c Wed Feb 22 01:50:13 2012 (r231988) > >> +++ head/lib/libthr/thread/thr_umtx.c Wed Feb 22 03:22:49 2012 (r231989) > >> @@ -200,20 +200,10 @@ int > >> + abstime != NULL ? (void *)(uintptr_t)((clockid<< 16) | UMTX_WAIT_ABSTIME) : 0, > > Please check that this shift does not lose any information (i.e., > > clockid>= 0&& clockid<= 0xFFFF) before doing it. > > Implementing clock_getcpuclockid() will require clockids greater than > > 65535 because such clockids contain a process id. > In which document said the clock id includes a process id ? I think the > clock_getcpuclockid() > is a simplified version of getrusage(). clock_getcpuclockid() lets you find a clock ID for the CPU time clock of a process. Usage could be like this: int error; pid_t pid; clockid_t clk; struct timespec ts; error = clock_getcpuclockid(pid, &clk); if (error == 0) if (clock_gettime(clk, &ts) == 0) printf("%lu.%09lu\n", (unsigned long)ts.tv_sec, (unsigned long)ts.tv_usec); One way to implement it is to reserve a PID_MAX sized subrange of clockid_t for this purpose. Similarly, pthread_getcpuclockid() lets you find a clock ID for the CPU time clock of a thread. These seem mostly useful for clock_getres(), clock_gettime() and possibly timer_create(). Besides, sem_timedwait() doesn't even let you specify a clock ID. -- Jilles Tjoelker
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