On Tue, Nov 15, 2016 at 03:22:59PM +0000, Patrick Bellasi wrote:
On 15-Nov 22:05, Leo Yan wrote:
But this code is delibrately written for WALT to update souce rq and destination rq statistics for workload. So currently I can simply revert double_lock_balance()/double_unlock_balance() for only using PELT signals, but for WALT I want to get some suggestion for the fixing, if we confirm this is a potential issue, this issue should exist both on Android common kernel 3.18 and 4.4.
AFAIK, in the (simplified) version of WALT posted on LKML before LPC [2] Vikram got ride of all the double loking. If the problem you reported is verified, than we should probably try to update AOSP WALT using the same locking schema used by the LKML posting.
[1] http://www2.comp.ufscar.br/lxr/source/Documentation/RCU/RTFP.txt#L176 [2] https://lkml.org/lkml/2016/10/28/84
Cheers Patrick
/*
- detach_task() -- detach the task for the migration specified in env
*/ static void detach_task(struct task_struct *p, struct lb_env *env) { lockdep_assert_held(&env->src_rq->lock);
deactivate_task(env->src_rq, p, 0); p->on_rq = TASK_ON_RQ_MIGRATING; double_lock_balance(env->src_rq, env->dst_rq); set_task_cpu(p, env->dst_cpu); double_unlock_balance(env->src_rq, env->dst_rq);}
I'm a bit worried that this unlocking business as part of the double-locking in detach_task() is not safe.
If the code looks anything like mainline in detach_tasks() (notice the s), I don't think it is safe.
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