Peter Zijlstra a81c69e149 RFC: FROMLIST: cgroup: avoid synchronize_sched() in __cgroup_procs_write() ... The current percpu-rwsem read side is entirely free of serializing insns at the cost of having a synchronize_sched() in the write path. The latency of the synchronize_sched() is too high for cgroups. The commit 1ed1328792 talks about the write path being a fairly cold path but this is not the case for Android which moves task to the foreground cgroup and back around binder IPC calls from foreground processes to background processes, so it is significantly hotter than human initiated operations. Switch cgroup_threadgroup_rwsem into the slow mode for now to avoid the problem, hopefully it should not be that slow after another commit 80127a3968 ("locking/percpu-rwsem: Optimize readers and reduce global impact"). We could just add rcu_sync_enter() into cgroup_init() but we do not want another synchronize_sched() at boot time, so this patch adds the new helper which doesn't block but currently can only be called before the first use. Cc: Tejun Heo <tj@kernel.org> Cc: Paul McKenney <paulmck@linux.vnet.ibm.com> Reported-by: John Stultz <john.stultz@linaro.org> Reported-by: Dmitry Shmidt <dimitrysh@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Oleg Nesterov <oleg@redhat.com> [jstultz: backported to 4.4] Change-Id: I34aa9c394d3052779b56976693e96d861bd255f2 Mailing-list-URL: https://lkml.org/lkml/2016/8/11/557 Signed-off-by: John Stultz <john.stultz@linaro.org>		2016-09-14 14:26:20 +05:30
..
acpi
asm-generic	Merge tag 'v4.4.17' into linux-linaro-lsk-v4.4	2016-08-11 12:15:51 +08:00
clocksource
crypto	crypto: af_alg - Allow af_af_alg_release_parent to be called on nokey path	2016-02-17 12:31:03 -08:00
drm	drm/ttm: Make ttm_bo_mem_compat available	2016-07-27 09:47:35 -07:00
dt-bindings
keys
kvm	KVM: arm/arm64: arch_timer: Preserve physical dist. active state on LR.active	2015-11-24 18:07:40 +01:00
linux	RFC: FROMLIST: cgroup: avoid synchronize_sched() in __cgroup_procs_write()	2016-09-14 14:26:20 +05:30
math-emu
media	videobuf2-core: Check user space planes array in dqbuf	2016-05-04 14:48:50 -07:00
memory
misc
net	ANDROID: net: fib: remove duplicate assignment	2016-08-18 18:56:03 +05:30
pcmcia
ras
rdma	IB/security: Restrict use of the write() interface	2016-05-04 14:48:48 -07:00
rxrpc
scsi	scsi: Add intermediate STARGET_REMOVE state to scsi_target_state	2016-06-01 12:15:54 -07:00
soc
sound	ALSA: rawmidi: Make snd_rawmidi_transmit() race-free	2016-02-17 12:30:58 -08:00
target	target: Fix WRITE_SAME/DISCARD conversion to linux 512b sectors	2016-03-09 15:34:51 -08:00
trace	trace: cpufreq: fix typo in min/max cpufreq	2016-04-07 16:50:03 +05:30
uapi	ANDROID: net: core: fix UID-based routing	2016-08-18 18:56:03 +05:30
video	Merge branch 'linux-linaro-lsk-v4.4' into linux-linaro-lsk-v4.4-android	2016-06-14 17:08:03 +08:00
xen	xen: Fix page <-> pfn conversion on 32 bit systems	2016-05-11 11:21:14 +02:00
Kbuild