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Subject: Re: svn commit: r339582 - head/sys/dev/sound/midi
To: Konstantin Belousov <kostikbel@gmail.com>
Cc: src-committers@freebsd.org, svn-src-all@freebsd.org,
 svn-src-head@freebsd.org
References: <201810220858.w9M8wSBZ039042@repo.freebsd.org>
 <20181022095131.GN5335@kib.kiev.ua>
 <cc0210c5-99c7-1153-0b32-4cfdc576970a@selasky.org>
 <20181022102016.GO5335@kib.kiev.ua>
From: Hans Petter Selasky <hps@selasky.org>
Message-ID: <e4859526-b49f-b46b-a754-1bf88ac22e40@selasky.org>
Date: Mon, 22 Oct 2018 12:26:46 +0200
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On 10/22/18 12:20 PM, Konstantin Belousov wrote:
> Then why do you need to re-acquire the mutex after uiomove ?

Hi,

Because the code is factored this way:

mtx_lock();
while (uio->uio_resid > 0) {
	do state checks()
	mtx_unlock();
	retval = uiomove();
	mtx_lock();
}
mtx_unlock();

Yes, you're right the last mtx_lock() can be optimised away. I'm leaving 
that to somebody else. This code typically is processing MIDI events at 
very slow rates like 8KBytes/s and does not need to be very fast.

--HPS