Messages in this thread Patch in this message |  | | Date | Sun, 6 Dec 2020 12:34:18 -0500 | From | Joel Fernandes <> | Subject | Re: [PATCH -tip 23/32] sched: Add a per-thread core scheduling interface |
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On Wed, Dec 02, 2020 at 04:47:17PM -0500, Chris Hyser wrote: > On Tue, Nov 17, 2020 at 06:19:53PM -0500, Joel Fernandes (Google) wrote: > > Add a per-thread core scheduling interface which allows a thread to share a > > core with another thread, or have a core exclusively for itself. > > > > ChromeOS uses core-scheduling to securely enable hyperthreading. This cuts > > down the keypress latency in Google docs from 150ms to 50ms while improving > > the camera streaming frame rate by ~3%. > > > > Inline is a patch for comment to extend this interface to make it more useful. > This patch would still need to provide doc and selftests updates as well. > > -chrish > > ---8<----------------------- [..] > diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h > index 217b048..f8e4e96 100644 > --- a/include/uapi/linux/prctl.h > +++ b/include/uapi/linux/prctl.h > @@ -250,5 +250,8 @@ struct prctl_mm_map { > > /* Request the scheduler to share a core */ > #define PR_SCHED_CORE_SHARE 59 > +# define PR_SCHED_CORE_CLEAR 0 /* clear core_sched cookie of pid */ > +# define PR_SCHED_CORE_SHARE_FROM 1 /* get core_sched cookie from pid */ > +# define PR_SCHED_CORE_SHARE_TO 2 /* push core_sched cookie to pid */ > > #endif /* _LINUX_PRCTL_H */ > diff --git a/kernel/sched/coretag.c b/kernel/sched/coretag.c > index 800c0f8..14feac1 100644 > --- a/kernel/sched/coretag.c > +++ b/kernel/sched/coretag.c > @@ -9,6 +9,7 @@ > */ > > #include "sched.h" > +#include "linux/prctl.h" > > /* > * Wrapper representing a complete cookie. The address of the cookie is used as > @@ -456,40 +457,45 @@ int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2) > } > > /* Called from prctl interface: PR_SCHED_CORE_SHARE */ > -int sched_core_share_pid(pid_t pid) > +int sched_core_share_pid(unsigned long flags, pid_t pid) > { > + struct task_struct *dest; > + struct task_struct *src; > struct task_struct *task; > int err; > > - if (pid == 0) { /* Recent current task's cookie. */ > - /* Resetting a cookie requires privileges. */ > - if (current->core_task_cookie) > - if (!capable(CAP_SYS_ADMIN)) > - return -EPERM; > - task = NULL; > - } else { > - rcu_read_lock(); > - task = pid ? find_task_by_vpid(pid) : current; > - if (!task) { > - rcu_read_unlock(); > - return -ESRCH; > - } > - > - get_task_struct(task); > - > - /* > - * Check if this process has the right to modify the specified > - * process. Use the regular "ptrace_may_access()" checks. > - */ > - if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) { > - rcu_read_unlock(); > - err = -EPERM; > - goto out; > - } > + rcu_read_lock(); > + task = find_task_by_vpid(pid); > + if (!task) { > rcu_read_unlock(); > + return -ESRCH; > } > > - err = sched_core_share_tasks(current, task); > + get_task_struct(task); > + > + /* > + * Check if this process has the right to modify the specified > + * process. Use the regular "ptrace_may_access()" checks. > + */ > + if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) { > + rcu_read_unlock(); > + err = -EPERM; > + goto out; > + } > + rcu_read_unlock(); > + > + if (flags == PR_SCHED_CORE_CLEAR) { > + dest = task; > + src = NULL; > + } else if (flags == PR_SCHED_CORE_SHARE_TO) { > + dest = task; > + src = current; > + } else if (flags == PR_SCHED_CORE_SHARE_FROM) { > + dest = current; > + src = task; > + }
Looks ok to me except the missing else { } clause you found. Also, maybe dest/src can be renamed to from/to to make meaning of variables more clear?
Also looking forward to the docs/test updates.
thanks!
- Joel
> + > + err = sched_core_share_tasks(dest, src); > out: > if (task) > put_task_struct(task); > diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c > index cffdfab..50c31f3 100644 > --- a/kernel/sched/debug.c > +++ b/kernel/sched/debug.c > @@ -1030,6 +1030,7 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns, > > #ifdef CONFIG_SCHED_CORE > __PS("core_cookie", p->core_cookie); > + __PS("core_task_cookie", p->core_task_cookie); > #endif > > sched_show_numa(p, m); > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index b3b89bd..eafb399 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1202,7 +1202,7 @@ void sched_core_dequeue(struct rq *rq, struct task_struct *p); > void sched_core_get(void); > void sched_core_put(void); > > -int sched_core_share_pid(pid_t pid); > +int sched_core_share_pid(unsigned long flags, pid_t pid); > int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2); > > #ifdef CONFIG_CGROUP_SCHED > diff --git a/kernel/sys.c b/kernel/sys.c > index 61a3c98..da52a0d 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -2530,9 +2530,13 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, > > error = (current->flags & PR_IO_FLUSHER) == PR_IO_FLUSHER; > break; > +#ifdef CONFIG_SCHED_CORE > case PR_SCHED_CORE_SHARE: > - error = sched_core_share_pid(arg2); > + if (arg4 || arg5) > + return -EINVAL; > + error = sched_core_share_pid(arg2, arg3); > break; > +#endif > default: > error = -EINVAL; > break;
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