Date: Fri, 3 Apr 2015 07:47:08 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Chris J Arges <chris.j.arges@canonical.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Rafael David Tinoco <inaddy@ubuntu.com>, Peter Anvin <hpa@zytor.com>,
        Jiang Liu <jiang.liu@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>, Jens Axboe <axboe@kernel.dk>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Gema Gomez <gema.gomez-solano@canonical.com>,
        the arch/x86 maintainers <x86@kernel.org>
Subject: Re: [PATCH] smp/call: Detect stuck CSD locks
Message-ID: <20150403054708.GA12316@gmail.com>
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 <20150402182607.GA8896@gmail.com>
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* Ingo Molnar <mingo@kernel.org> wrote:

> +static void csd_lock_wait(struct call_single_data *csd, int cpu)
>  {
> -	while (csd->flags & CSD_FLAG_LOCK)
> +	int bug_id = 0;
> +	u64 ts0, ts1, ts_delta;
> +
> +	ts0 = jiffies_to_msecs(jiffies);

Note that while 'jiffies' is a global variable, it's read-mostly 
accessed, so it is a pretty cheap way to acquire a timestamp in such a 
simple polling context that has irqs enabled.

Thanks,

	Ingo
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