linux-kernel - [PATCH v2 0/5] sched: Add on_rq states and remove several double rq locks

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 26 Jul 2014 18:58:48 +0400
From:	Kirill Tkhai <tkhai@...dex.ru>
To:	linux-kernel@...r.kernel.org
Cc:	nicolas.pitre@...aro.org, peterz@...radead.org, pjt@...gle.com,
	oleg@...hat.com, rostedt@...dmis.org, umgwanakikbuti@...il.com,
	ktkhai@...allels.com, tim.c.chen@...ux.intel.com, mingo@...nel.org
Subject: [PATCH v2 0/5] sched: Add on_rq states and remove several double rq
 locks

This series aims to get rid of some places where locks of two RQs are held
at the same time.

Patch [1/5] is a preparation/cleanup. It replaces old (.on_rq == 1) with new
(.on_rq == ONRQ_QUEUED) everywhere. No functional changes.

Patch [2/5] is main in the series. It introduces new state: ONRQ_MIGRATING
and teaches scheduler to understand it (we need a little changes predominantly
in try_to_wake_up()). This will be used in the following way:

        (we are changing task's rq)

        raw_spin_lock(&src_rq->lock);
        dequeue_task(src_rq, p, 0);
        p->on_rq = ONRQ_MIGRATING;
        set_task_cpu(p, dst_cpu);
        raw_spin_unlock(&src_rq->lock);

        raw_spin_lock(&dst_rq->lock);
        p->on_rq = ONRQ_QUEUED;
        enqueue_task(dst_rq, p, 0);
        raw_spin_unlock(&dst_rq->lock);

Patches [3-5/5] remove double locks and use new ONRQ_MIGRATING state.
They allow unlocked using of 3-4 function, which looks safe for me.

The series doesn't add any overhead, and it shouldn't worsen performance,
I think. It improves granularity, and it's possible to imagine situations,
which will be happier without double rq lock.

v2: Changes in [2/5] and [5/5].

---

Kirill Tkhai (5):
      sched: Wrapper for checking task_struct's .on_rq
      sched: Teach scheduler to understand ONRQ_MIGRATING state
      sched: Remove double_rq_lock() from __migrate_task()
      sched/fair: Remove double_lock_balance() from active_load_balance_cpu_stop()
      sched/fair: Remove double_lock_balance() from load_balance()


 kernel/sched/core.c      |  123 +++++++++++++++++++++++--------------
 kernel/sched/deadline.c  |   14 ++--
 kernel/sched/fair.c      |  155 ++++++++++++++++++++++++++++++----------------
 kernel/sched/rt.c        |   16 ++---
 kernel/sched/sched.h     |   13 ++++
 kernel/sched/stop_task.c |    2 -
 6 files changed, 206 insertions(+), 117 deletions(-)

--
Signed-off-by: Kirill Tkhai <ktkhai@...allels.com>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/