Date: Tue, 23 Feb 2010 11:13:11 -0800 From: Julian Elischer <julian@elischer.org> To: Shrivatsan <shrivatsan_v@yahoo.com> Cc: freebsd-hackers@FreeBSD.org, shrivatsan@gmail.com Subject: Re: sched_lock mutex and sleepq_wait Message-ID: <4B8428C7.8010705@elischer.org> In-Reply-To: <986041.3700.qm@web112005.mail.gq1.yahoo.com> References: <986041.3700.qm@web112005.mail.gq1.yahoo.com>
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Shrivatsan wrote:
> Hi,
>
> I am trying to understand how msleep() routine suspends the currently
> executing thread. I see that msleep() calls sleepq_wait().
>
> What I don't understand here is the way in which sched_lock mutex is
> handled.
>
> I took the following snippet from FreeBSD 6:
>
> sleepq_wait(void *wchan)
> {
> MPASS(!(curthread->td_flags & TDF_SINTR));
> mtx_lock_spin(&sched_lock);
> sleepq_switch(wchan);
----we sleep here-----
some other thread runs, When it wakes up it magicall owns the
schedlock which it releases. then it sleeps and locks schedlock
again.A
----- we get run.. magically the schedlock is changed so that we
own it. now we return, maybe 5 minutes later and must free it.
> mtx_unlock_spin(&sched_lock);
> }
>
> sched_lock mutex is held, and sleepq_switch() eventually calls
> cpu_switch() which switches to a new thread.
>
> I don't exactly understand when the sched_lock mutex is released.
>
> Can someone please help me?
>
> Thanks,
> -shrivatsan
>
>
>
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