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Subject: Re: svn commit: r308424 - head/sys/arm/broadcom/bcm2835
To: John Baldwin <jhb@freebsd.org>
References: <201611071738.uA7HceYu045944@repo.freebsd.org>
 <680D84F2-65BF-48DD-8D11-311B1F65A634@freebsd.org>
 <c7cd871d-9007-6de4-7063-2680e259713f@selasky.org>
 <3214848.geWV8qu7rM@ralph.baldwin.cx>
Cc: Oleksandr Tymoshenko <gonzo@freebsd.org>, src-committers@freebsd.org,
 svn-src-all@freebsd.org, svn-src-head@freebsd.org
From: Hans Petter Selasky <hps@selasky.org>
Message-ID: <5c170b6b-1189-4712-ffdd-653cc6b8c59e@selasky.org>
Date: Wed, 9 Nov 2016 17:10:09 +0100
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Hi,

On 11/09/16 16:02, John Baldwin wrote:
 > On the other hand, doing the wakeup outside of the lock
> avoids preempting during the wakeup only to immediately block on the lock and
> switch back to the thread that did the wakeup.

This can be predicted and avoided by the turnstiles iff cv_signal() is 
used under a lock. Else not.

Won't doing the wakeup outside the lock cause double preemtion? First at 
mtx_unlock() and then inside cv_signal()/cv_broadcast().

--HPS