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Date: Mon, 9 Nov 2020 18:30:12 -0500
From: chris hyser <chris.hyser@...cle.com>
To: "Joel Fernandes (Google)" <joel@...lfernandes.org>,
Nishanth Aravamudan <naravamudan@...italocean.com>,
Julien Desfossez <jdesfossez@...italocean.com>,
Peter Zijlstra <peterz@...radead.org>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Vineeth Pillai <viremana@...ux.microsoft.com>,
Aaron Lu <aaron.lwe@...il.com>,
Aubrey Li <aubrey.intel@...il.com>, tglx@...utronix.de,
linux-kernel@...r.kernel.org
Cc: mingo@...nel.org, torvalds@...ux-foundation.org,
fweisbec@...il.com, keescook@...omium.org, kerrnel@...gle.com,
Phil Auld <pauld@...hat.com>,
Valentin Schneider <valentin.schneider@....com>,
Mel Gorman <mgorman@...hsingularity.net>,
Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
Paolo Bonzini <pbonzini@...hat.com>, vineeth@...byteword.org,
Chen Yu <yu.c.chen@...el.com>,
Christian Brauner <christian.brauner@...ntu.com>,
Agata Gruza <agata.gruza@...el.com>,
Antonio Gomez Iglesias <antonio.gomez.iglesias@...el.com>,
graf@...zon.com, konrad.wilk@...cle.com, dfaggioli@...e.com,
pjt@...gle.com, rostedt@...dmis.org, derkling@...gle.com,
benbjiang@...cent.com,
Alexandre Chartre <alexandre.chartre@...cle.com>,
James.Bottomley@...senpartnership.com, OWeisse@...ch.edu,
Dhaval Giani <dhaval.giani@...cle.com>,
Junaid Shahid <junaids@...gle.com>, jsbarnes@...gle.com,
Aubrey Li <aubrey.li@...ux.intel.com>,
"Paul E. McKenney" <paulmck@...nel.org>,
Tim Chen <tim.c.chen@...el.com>
Subject: Re: [PATCH v8 -tip 17/26] sched: Split the cookie and setup per-task
cookie on fork
On 11/4/20 5:30 PM, chris hyser wrote:
> On 10/19/20 9:43 PM, Joel Fernandes (Google) wrote:
>> In order to prevent interference and clearly support both per-task and CGroup
>> APIs, split the cookie into 2 and allow it to be set from either per-task, or
>> CGroup API. The final cookie is the combined value of both and is computed when
>> the stop-machine executes during a change of cookie.
>>
>> Also, for the per-task cookie, it will get weird if we use pointers of any
>> emphemeral objects. For this reason, introduce a refcounted object who's sole
>> purpose is to assign unique cookie value by way of the object's pointer.
>>
>> While at it, refactor the CGroup code a bit. Future patches will introduce more
>> APIs and support.
>>
>> Tested-by: Julien Desfossez <jdesfossez@...italocean.com>
>> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
>> ---
>> include/linux/sched.h | 2 +
>> kernel/sched/core.c | 241 ++++++++++++++++++++++++++++++++++++++++--
>> kernel/sched/debug.c | 4 +
>> 3 files changed, 236 insertions(+), 11 deletions(-)
>>
>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> index fe6f225bfbf9..c6034c00846a 100644
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -688,6 +688,8 @@ struct task_struct {
>> #ifdef CONFIG_SCHED_CORE
>> struct rb_node core_node;
>> unsigned long core_cookie;
>> + unsigned long core_task_cookie;
>> + unsigned long core_group_cookie;
>> unsigned int core_occupation;
>> #endif
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index bab4ea2f5cd8..30a9e4cb5ce1 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -346,11 +346,14 @@ void sched_core_put(void)
>> mutex_unlock(&sched_core_mutex);
>> }
>> +static int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2);
>> +
>> #else /* !CONFIG_SCHED_CORE */
>> static inline void sched_core_enqueue(struct rq *rq, struct task_struct *p) { }
>> static inline void sched_core_dequeue(struct rq *rq, struct task_struct *p) { }
>> static bool sched_core_enqueued(struct task_struct *task) { return false; }
>> +static int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2) { }
>> #endif /* CONFIG_SCHED_CORE */
>> @@ -3583,6 +3586,20 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
>> #endif
>> #ifdef CONFIG_SCHED_CORE
>> RB_CLEAR_NODE(&p->core_node);
>> +
>> + /*
>> + * Tag child via per-task cookie only if parent is tagged via per-task
>> + * cookie. This is independent of, but can be additive to the CGroup tagging.
>> + */
>> + if (current->core_task_cookie) {
>> +
>> + /* If it is not CLONE_THREAD fork, assign a unique per-task tag. */
>> + if (!(clone_flags & CLONE_THREAD)) {
>> + return sched_core_share_tasks(p, p);
>> + }
>> + /* Otherwise share the parent's per-task tag. */
>> + return sched_core_share_tasks(p, current);
>> + }
>> #endif
>> return 0;
>> }
sched_core_share_tasks() looks at the value of the new tasks core_task_cookie which is non-zero on a
process or thread clone and causes underflow for both the enable flag itself and for cookie ref counts.
So just zero it in __sched_fork().
-chrish
------
sched: zero out the core scheduling cookie on clone
As the cookie is reference counted, even if inherited, zero this and allow
explicit sharing.
Signed-off-by: Chris Hyser <chris.hyser@...cle.com>
---
kernel/sched/core.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fd3cc03..2af0ea6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3378,6 +3378,9 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
p->capture_control = NULL;
#endif
init_numa_balancing(clone_flags, p);
+#ifdef CONFIG_SCHED_CORE
+ p->core_task_cookie = 0;
+#endif
#ifdef CONFIG_SMP
p->wake_entry.u_flags = CSD_TYPE_TTWU;
#endif
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