linux-kernel - Re: [PATCH] sched/fair: sync expires_seq in distribute_cfs

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Date:   Mon, 30 Jul 2018 13:28:51 +0800
From:   Xunlei Pang <xlpang@...ux.alibaba.com>
To:     Cong Wang <xiyou.wangcong@...il.com>, linux-kernel@...r.kernel.org
Cc:     Ben Segall <bsegall@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] sched/fair: sync expires_seq in distribute_cfs_runtime()

Hi Cong,

On 7/28/18 8:24 AM, Cong Wang wrote:
> Each time we sync cfs_rq->runtime_expires with cfs_b->runtime_expires,
> we should sync its ->expires_seq too. However it is missing
> for distribute_cfs_runtime(), especially the slack timer call path.

I don't think it's a problem, as expires_seq will get synced in
assign_cfs_rq_runtime().

Thanks,
Xunlei

> 
> Fixes: 512ac999d275 ("sched/fair: Fix bandwidth timer clock drift condition")
> Cc: Xunlei Pang <xlpang@...ux.alibaba.com>
> Cc: Ben Segall <bsegall@...gle.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> ---
>  kernel/sched/fair.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 2f0a0be4d344..910c50db3d74 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4857,7 +4857,7 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
>  }
>  
>  static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
> -		u64 remaining, u64 expires)
> +		u64 remaining, u64 expires, int expires_seq)
>  {
>  	struct cfs_rq *cfs_rq;
>  	u64 runtime;
> @@ -4880,6 +4880,7 @@ static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
>  
>  		cfs_rq->runtime_remaining += runtime;
>  		cfs_rq->runtime_expires = expires;
> +		cfs_rq->expires_seq = expires_seq;
>  
>  		/* we check whether we're throttled above */
>  		if (cfs_rq->runtime_remaining > 0)
> @@ -4905,7 +4906,7 @@ static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
>  static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
>  {
>  	u64 runtime, runtime_expires;
> -	int throttled;
> +	int throttled, expires_seq;
>  
>  	/* no need to continue the timer with no bandwidth constraint */
>  	if (cfs_b->quota == RUNTIME_INF)
> @@ -4933,6 +4934,7 @@ static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
>  	cfs_b->nr_throttled += overrun;
>  
>  	runtime_expires = cfs_b->runtime_expires;
> +	expires_seq = cfs_b->expires_seq;
>  
>  	/*
>  	 * This check is repeated as we are holding onto the new bandwidth while
> @@ -4946,7 +4948,7 @@ static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
>  		raw_spin_unlock(&cfs_b->lock);
>  		/* we can't nest cfs_b->lock while distributing bandwidth */
>  		runtime = distribute_cfs_runtime(cfs_b, runtime,
> -						 runtime_expires);
> +						 runtime_expires, expires_seq);
>  		raw_spin_lock(&cfs_b->lock);
>  
>  		throttled = !list_empty(&cfs_b->throttled_cfs_rq);
> @@ -5055,6 +5057,7 @@ static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
>  static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b)
>  {
>  	u64 runtime = 0, slice = sched_cfs_bandwidth_slice();
> +	int expires_seq;
>  	u64 expires;
>  
>  	/* confirm we're still not at a refresh boundary */
> @@ -5068,12 +5071,13 @@ static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b)
>  		runtime = cfs_b->runtime;
>  
>  	expires = cfs_b->runtime_expires;
> +	expires_seq = cfs_b->expires_seq;
>  	raw_spin_unlock(&cfs_b->lock);
>  
>  	if (!runtime)
>  		return;
>  
> -	runtime = distribute_cfs_runtime(cfs_b, runtime, expires);
> +	runtime = distribute_cfs_runtime(cfs_b, runtime, expires, expires_seq);
>  
>  	raw_spin_lock(&cfs_b->lock);
>  	if (expires == cfs_b->runtime_expires)
>