While going through enqueue/dequeue to review the movement of
set_curr_task() I noticed that the (2nd) update_min_vruntime() call in
dequeue_entity() is suspect.
It turns out, its actually wrong because it will consider
cfs_rq->curr, which could be the entry we just normalized. This mixes
different vruntime forms and leads to fail.
The purpose of the second update_min_vruntime() is to move
min_vruntime forward if the entity we just removed is the one that was
holding it back; _except_ for the DEQUEUE_SAVE case, because then we
know its a temporary removal and it will come back.
However, since we do put_prev_task() _after_ dequeue(), cfs_rq->curr
will still be set (and per the above, can be tranformed into a
different unit), so update_min_vruntime() should also consider
curr->on_rq. This also fixes another corner case where the enqueue
(which also does update_curr()->update_min_vruntime()) happens on the
rq->lock break in schedule(), between dequeue and put_prev_task.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Fixes: 1e87623178 ("sched: Fix ->min_vruntime calculation in dequeue_entity()")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Almost all scheduler functions update state with the following
pattern:
if (queued)
dequeue_task(rq, p, DEQUEUE_SAVE);
if (running)
put_prev_task(rq, p);
/* update state */
if (queued)
enqueue_task(rq, p, ENQUEUE_RESTORE);
if (running)
set_curr_task(rq, p);
set_user_nice() however misses the running part, cure this.
This was found by asserting we never enqueue 'current'.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
select_idle_siblings() is a known pain point for a number of
workloads; it either does too much or not enough and sometimes just
does plain wrong.
This rewrite attempts to address a number of issues (but sadly not
all).
The current code does an unconditional sched_domain iteration; with
the intent of finding an idle core (on SMT hardware). The problems
which this patch tries to address are:
- its pointless to look for idle cores if the machine is real busy;
at which point you're just wasting cycles.
- it's behaviour is inconsistent between SMT and !SMT hardware in
that !SMT hardware ends up doing a scan for any idle CPU in the LLC
domain, while SMT hardware does a scan for idle cores and if that
fails, falls back to a scan for idle threads on the 'target' core.
The new code replaces the sched_domain scan with 3 explicit scans:
1) search for an idle core in the LLC
2) search for an idle CPU in the LLC
3) search for an idle thread in the 'target' core
where 1 and 3 are conditional on SMT support and 1 and 2 have runtime
heuristics to skip the step.
Step 1) is conditional on sd_llc_shared->has_idle_cores; when a cpu
goes idle and sd_llc_shared->has_idle_cores is false, we scan all SMT
siblings of the CPU going idle. Similarly, we clear
sd_llc_shared->has_idle_cores when we fail to find an idle core.
Step 2) tracks the average cost of the scan and compares this to the
average idle time guestimate for the CPU doing the wakeup. There is a
significant fudge factor involved to deal with the variability of the
averages. Esp. hackbench was sensitive to this.
Step 3) is unconditional; we assume (also per step 1) that scanning
all SMT siblings in a core is 'cheap'.
With this; SMT systems gain step 2, which cures a few benchmarks --
notably one from Facebook.
One 'feature' of the sched_domain iteration, which we preserve in the
new code, is that it would start scanning from the 'target' CPU,
instead of scanning the cpumask in cpu id order. This avoids multiple
CPUs in the LLC scanning for idle to gang up and find the same CPU
quite as much. The down side is that tasks can end up hopping across
the LLC for no apparent reason.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Since struct sched_domain is strictly per cpu; introduce a structure
that is shared between all 'identical' sched_domains.
Limit to SD_SHARE_PKG_RESOURCES domains for now, as we'll only use it
for shared cache state; if another use comes up later we can easily
relax this.
While the sched_group's are normally shared between CPUs, these are
not natural to use when we need some shared state on a domain level --
since that would require the domain to have a parent, which is not a
given.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
There is no point in doing a call_rcu() for each domain, only do a
callback for the root sched domain and clean up the entire set in one
go.
Also make the entire call chain be called destroy_sched_domain*() to
remove confusion with the free_sched_domains() call, which does an
entirely different thing.
Both cpu_attach_domain() callers of destroy_sched_domain() can live
without the call_rcu() because at those points the sched_domain hasn't
been published yet.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Otherwise this logic only works if mode is "compatible" with another
exclusive waiter.
If some wq has both TASK_INTERRUPTIBLE and TASK_UNINTERRUPTIBLE waiters,
abort_exclusive_wait() won't wait an uninterruptible waiter.
The main user is __wait_on_bit_lock() and currently it is fine but only
because TASK_KILLABLE includes TASK_UNINTERRUPTIBLE and we do not have
lock_page_interruptible() yet.
Just use TASK_NORMAL and remove the "mode" arg from abort_exclusive_wait().
Yes, this means that (say) wake_up_interruptible() can wake up the non-
interruptible waiter(s), but I think this is fine. And in fact I think
that abort_exclusive_wait() must die, see the next change.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Neil Brown <neilb@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20160906140047.GA6157@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Pull cgroup fixes from Tejun Heo:
"Three late fixes for cgroup: Two cpuset ones, one trivial and the
other pretty obscure, and a cgroup core fix for a bug which impacts
cgroup v2 namespace users"
* 'for-4.8-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
cgroup: fix invalid controller enable rejections with cgroup namespace
cpuset: fix non static symbol warning
cpuset: handle race between CPU hotplug and cpuset_hotplug_work
Pull tracefs fixes from Steven Rostedt:
"Al Viro has been looking at the tracefs code, and has pointed out some
issues. This contains one fix by me and one by Al. I'm sure that
he'll come up with more but for now I tested these patches and they
don't appear to have any negative impact on tracing"
* tag 'trace-v4.8-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
fix memory leaks in tracing_buffers_splice_read()
tracing: Move mutex to protect against resetting of seq data
The iter->seq can be reset outside the protection of the mutex. So can
reading of user data. Move the mutex up to the beginning of the function.
Fixes: d7350c3f45 ("tracing/core: make the read callbacks reentrants")
Cc: stable@vger.kernel.org # 2.6.30+
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Pull perf fixes from Thomas Gleixner:
"Three fixlets for perf:
- add a missing NULL pointer check in the intel BTS driver
- make BTS an exclusive PMU because BTS can only handle one event at
a time
- ensure that exclusive events are limited to one PMU so that several
exclusive events can be scheduled on different PMU instances"
* 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
perf/core: Limit matching exclusive events to one PMU
perf/x86/intel/bts: Make it an exclusive PMU
perf/x86/intel/bts: Make sure debug store is valid
Frederic Weisbecker
Peter Zijlstra
Vincent Guittot
Oleg Nesterov
Dietmar Eggemann
Tim Chen
Ingo Molnar
Linus Torvalds
Al Viro
Steven Rostedt (Red Hat)