From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 29703 invoked by alias); 14 Dec 2018 20:55:24 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Received: (qmail 28248 invoked by uid 89); 14 Dec 2018 20:55:23 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-26.9 required=5.0 tests=BAYES_00,GIT_PATCH_0,GIT_PATCH_1,GIT_PATCH_2,GIT_PATCH_3,RCVD_IN_DNSWL_NONE autolearn=ham version=3.3.2 spammy=explained, bullet, opposed, sched_yield X-HELO: mail-qt1-f196.google.com Return-Path: Subject: Re: [PATCH] manual: Document lack of conformance of sched_* functions [BZ #14829] To: Florian Weimer , libc-alpha@sourceware.org References: <87sgz9fq53.fsf@oldenburg2.str.redhat.com> From: Carlos O'Donell Openpgp: preference=signencrypt Message-ID: <74c5309f-ca7a-ae8b-5704-86329525cfde@redhat.com> Date: Fri, 14 Dec 2018 20:57:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1 MIME-Version: 1.0 In-Reply-To: <87sgz9fq53.fsf@oldenburg2.str.redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-SW-Source: 2018-12/txt/msg00501.txt.bz2 On 12/7/18 8:00 AM, Florian Weimer wrote: > On Linux, we define _POSIX_PRIORITY_SCHEDULING, but functions such > as sched_setparam and sched_setscheduler apply to individual threads, > not processes. I agree. This has always been a long-standing issue that has bothered me. Please accept my gracious thanks for fixing this. I wish we could do more, but we are limited by the underlying OS and how the that maps into POSIX. I'd like to see a v2 of this, and I'll review the text again. Thanks. > 2018-12-07 Florian Weimer > > [BZ #14829] > * manual/resource.texi (Basic Scheduling Functions): Add > portability note. Change process to task throughout the section. > Remove incorrect comment about sched_yield as it affects > tasks/threads, not entire processes. I think we need a *big* comment in sysdeps/unix/sysv/linux/bits/posix_opt.h around the define of _POSIX_PRIORITY_SCHEDULING which says: /* On Linux we do not conform to the POSIX requirements for setting _POSIX_PRIORITY_SCHEDULING, and it should be set to -1, but it has been enabled for so long that we cannot risk setting it to -1 without serious issues arising with existing applications, so we leave it enabled even though on Linux the APIs all take thread IDs. Please see bug 14829. */ What do you think? > diff --git a/manual/resource.texi b/manual/resource.texi > index 8bc2a803d4..f02192475a 100644 > --- a/manual/resource.texi > +++ b/manual/resource.texi > @@ -750,6 +750,14 @@ policy, if anything, only fine tunes the effect of that priority. > > The symbols in this section are declared by including file @file{sched.h}. > > +@strong{Portability Note:} In POSIX, the @code{pid_t} arguments of the > +functions below refer to process IDs. On Linux, they are actually > +thread IDs, and control how specific threads are scheduled with > +regards to the entire system. The resulting behavior does not conform > +to POSIX. This is why the following description refers to tasks and > +tasks IDs, and not processes and process IDs. > +@c https://sourceware.org/bugzilla/show_bug.cgi?id=14829 OK. Should we also mention that PTHREAD_SCOPE_PROCESS is entirely unsupported by glibc on Linux? > + > @deftp {Data Type} {struct sched_param} > @standards{POSIX, sched.h} > This structure describes an absolute priority. > @@ -765,11 +773,11 @@ absolute priority value > @c Direct syscall, Linux only. > > This function sets both the absolute priority and the scheduling policy > -for a process. > +for a task. OK. > > It assigns the absolute priority value given by @var{param} and the > -scheduling policy @var{policy} to the process with Process ID @var{pid}, > -or the calling process if @var{pid} is zero. If @var{policy} is > +scheduling policy @var{policy} to the task with ID @var{pid}, > +or the calling task if @var{pid} is zero. If @var{policy} is OK. > negative, @code{sched_setscheduler} keeps the existing scheduling policy. > > The following macros represent the valid values for @var{policy}: > @@ -795,20 +803,20 @@ to this function are: > @item EPERM > @itemize @bullet > @item > -The calling process does not have @code{CAP_SYS_NICE} permission and > +The calling task does not have @code{CAP_SYS_NICE} permission and OK. > @var{policy} is not @code{SCHED_OTHER} (or it's negative and the > existing policy is not @code{SCHED_OTHER}. > > @item > -The calling process does not have @code{CAP_SYS_NICE} permission and its > -owner is not the target process' owner. I.e., the effective uid of the > -calling process is neither the effective nor the real uid of process > +The calling task does not have @code{CAP_SYS_NICE} permission and its > +owner is not the target task's owner. I.e., the effective uid of the > +calling task is neither the effective nor the real uid of task OK. > @var{pid}. > @c We need a cross reference to the capabilities section, when written. > @end itemize > > @item ESRCH > -There is no process with pid @var{pid} and @var{pid} is not zero. > +There is no task with pid @var{pid} and @var{pid} is not zero. OK. > > @item EINVAL > @itemize @bullet > @@ -835,8 +843,8 @@ tell you what the valid range is. > @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} > @c Direct syscall, Linux only. > > -This function returns the scheduling policy assigned to the process with > -Process ID (pid) @var{pid}, or the calling process if @var{pid} is zero. > +This function returns the scheduling policy assigned to the task with > +ID @var{pid}, or the calling task if @var{pid} is zero. OK. > > The return value is the scheduling policy. See > @code{sched_setscheduler} for the possible values. > @@ -849,7 +857,7 @@ The @code{errno} values specific to this function are: > @table @code > > @item ESRCH > -There is no process with pid @var{pid} and it is not zero. > +There is no task with pid @var{pid} and it is not zero. OK. > > @item EINVAL > @var{pid} is negative. > @@ -869,7 +877,7 @@ absolute priority, use @code{sched_getparam}. > @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} > @c Direct syscall, Linux only. > > -This function sets a process' absolute priority. > +This function sets a task's absolute priority. OK. > > It is functionally identical to @code{sched_setscheduler} with > @var{policy} = @code{-1}. > @@ -883,13 +891,13 @@ It is functionally identical to @code{sched_setscheduler} with > @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} > @c Direct syscall, Linux only. > > -This function returns a process' absolute priority. > +This function returns a task's absolute priority. OK. > > -@var{pid} is the Process ID (pid) of the process whose absolute priority > -you want to know. > +@var{pid} is the task ID of the task whose absolute priority you want > +to know. Ok. > > @var{param} is a pointer to a structure in which the function stores the > -absolute priority of the process. > +absolute priority of the task. OK. > > On success, the return value is @code{0}. Otherwise, it is @code{-1} > and @code{errno} is set accordingly. The @code{errno} values specific > @@ -898,7 +906,7 @@ to this function are: > @table @code > > @item ESRCH > -There is no process with pid @var{pid} and it is not zero. > +There is no task with ID @var{pid} and it is not zero. OK. > > @item EINVAL > @var{pid} is negative. > @@ -914,7 +922,7 @@ There is no process with pid @var{pid} and it is not zero. > @c Direct syscall, Linux only. > > This function returns the lowest absolute priority value that is > -allowable for a process with scheduling policy @var{policy}. > +allowable for a task with scheduling policy @var{policy}. OK. > > On Linux, it is 0 for SCHED_OTHER and 1 for everything else. > > @@ -935,7 +943,7 @@ to this function are: > @c Direct syscall, Linux only. > > This function returns the highest absolute priority value that is > -allowable for a process that with scheduling policy @var{policy}. > +allowable for a task that with scheduling policy @var{policy}. OK. > > On Linux, it is 0 for SCHED_OTHER and 99 for everything else. > > @@ -956,8 +964,8 @@ to this function are: > @c Direct syscall, Linux only. > > This function returns the length of the quantum (time slice) used with > -the Round Robin scheduling policy, if it is used, for the process with > -Process ID @var{pid}. > +the Round Robin scheduling policy, if it is used, for the task with > +task ID @var{pid}. OK. > > It returns the length of time as @var{interval}. > @c We need a cross-reference to where timespec is explained. But that > @@ -980,18 +988,18 @@ function, so there are no specific @code{errno} values. > @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} > @c Direct syscall on Linux; alias to swtch on HURD. > > -This function voluntarily gives up the process' claim on the CPU. > +This function voluntarily gives up the task's claim on the CPU. OK. > > -Technically, @code{sched_yield} causes the calling process to be made > +Technically, @code{sched_yield} causes the calling task to be made OK. > immediately ready to run (as opposed to running, which is what it was > before). This means that if it has absolute priority higher than 0, it > -gets pushed onto the tail of the queue of processes that share its > +gets pushed onto the tail of the queue of tasks that share its OK. > absolute priority and are ready to run, and it will run again when its > turn next arrives. If its absolute priority is 0, it is more > complicated, but still has the effect of yielding the CPU to other > -processes. > +tasks. OK. > > -If there are no other processes that share the calling process' absolute > +If there are no other tasks that share the calling task's absolute > priority, this function doesn't have any effect. OK. > > To the extent that the containing program is oblivious to what other > -- Cheers, Carlos.