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Date:   Tue, 29 Jan 2019 11:44:31 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Suren Baghdasaryan <surenb@google.com>
Cc:     gregkh@linuxfoundation.org, tj@kernel.org, lizefan@huawei.com,
        hannes@cmpxchg.org, axboe@kernel.dk, dennis@kernel.org,
        dennisszhou@gmail.com, mingo@redhat.com, akpm@linux-foundation.org,
        corbet@lwn.net, cgroups@vger.kernel.org, linux-mm@kvack.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@android.com
Subject: Re: [PATCH v3 5/5] psi: introduce psi monitor
Message-ID: <20190129104431.GJ28467@hirez.programming.kicks-ass.net>
References: <20190124211518.244221-1-surenb@google.com>
 <20190124211518.244221-6-surenb@google.com>
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On Thu, Jan 24, 2019 at 01:15:18PM -0800, Suren Baghdasaryan wrote:
>  static void psi_update_work(struct work_struct *work)
>  {
>  	struct delayed_work *dwork;
>  	struct psi_group *group;
> +	bool first_pass = true;
> +	u64 next_update;
> +	u32 change_mask;
> +	int polling;
>  	bool nonidle;
> +	u64 now;
>  
>  	dwork = to_delayed_work(work);
>  	group = container_of(dwork, struct psi_group, clock_work);
>  
> +	now = sched_clock();
> +
> +	mutex_lock(&group->update_lock);

actually acquiring a mutex can take a fairly long while; would it not
make more sense to take the @now timestanp _after_ it, instead of
before?