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Subject: Re: td_swvoltick
To: Konstantin Belousov <kostikbel@gmail.com>
Cc: FreeBSD Current <freebsd-current@FreeBSD.org>
References: <603d2786-86be-583c-9ff6-d8d73eddf77e@vangyzen.net>
 <20180112193659.GL1684@kib.kiev.ua>
From: Eric van Gyzen <eric@vangyzen.net>
Message-ID: <b6a1b076-1e2f-e0f4-8934-6ed94ee796ae@vangyzen.net>
Date: Fri, 12 Jan 2018 16:36:56 -0600
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On 01/12/2018 13:36, Konstantin Belousov wrote:
> On Fri, Jan 12, 2018 at 01:31:41PM -0600, Eric van Gyzen wrote:
>> should_yield() compares thread::td_swvoltick to 'ticks' to determine
>> whether a thread is hogging and should yield.  Since td_swvoltick
>> records 'ticks' /before/ the actual context switch, the calculation in
>> should_yield() includes any time that the thread was switched out.  It
>> seems that should_yield() wants to know how long the thread has actually
>> been running.  Therefore, td_swvoltick should record 'ticks' /after/
>> sched_switch() returns.
>>
>> Does this make sense, or am I missing something?
> Yes, it does make sense to me.

Thanks, Kostik.

If anyone else is interested:  https://reviews.freebsd.org/D13892

>>
>> If this makes sense, I would probably keep the current assignment in
>> mi_switch() and simply add a second assignment after the call to
>> sched_switch().  That way, db_show_thread will still show useful data
>> for sleeping threads.  I would do the same for td_swinvolticks.
>>
>> I'll be happy to make the change myself.  I just want a sanity check
>> before I bother.
>>
>> Thanks in advance,
>>
>> Eric