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Date: Sun, 15 May 2016 10:14:39 +0800
From: Yuyang Du <yuyang.du@intel.com>
To: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        linux-kernel@vger.kernel.org, Byungchul Park <byungchul.park@lge.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Luca Abeni <luca.abeni@unitn.it>,
        "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
        Rik van Riel <riel@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
        Wanpeng Li <wanpeng.li@hotmail.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Mike Galbraith <umgwanakikbuti@gmail.com>
Subject: Re: [RFC][PATCH 5/5] sched/core: Add debug code to catch missing
 update_rq_clock()
Message-ID: <20160515021439.GC8790@intel.com>
References: <1463082593-27777-1-git-send-email-matt@codeblueprint.co.uk>
 <1463082593-27777-6-git-send-email-matt@codeblueprint.co.uk>
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Hi Matt,

Thanks for Ccing me.

I am indeed interested, because I recently encountered an rq clock
issue, which is that the clock jumps about 200ms when I was
experimenting the "flat util hierarchy" patches, which really annoyed
me, and I had to stop to figure out what is wrong (but haven't yet
figured out ;))

First, this patchset does not solve my problem, but never mind, by
reviewing your patches, I have some comments:

On Thu, May 12, 2016 at 08:49:53PM +0100, Matt Fleming wrote:
>  
> -	rq->clock_skip_update = 0;
> +	/* Clear ACT, preserve everything else */
> +	rq->clock_update_flags ^= RQCF_ACT_SKIP;

The comment says "Clear ACT", but this is really xor, and I am not sure
this is even what you want.

In addition, would it be simpler to do this?

update_rq_clock()
	if (flags & RQCF_ACT_SKIP)
		flags <<= 1; /* effective skip is an update */
		return;

	flags = RQCF_UPDATED;

Thanks,
Yuyang