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Date:      Tue, 21 Jan 2014 15:12:30 -0700
From:      Scott Long <scott4long@yahoo.com>
To:        John Baldwin <jhb@freebsd.org>
Cc:        src-committers@freebsd.org, Neel Natu <neel@freebsd.org>, svn-src-all@freebsd.org, Rui Paulo <rpaulo@felyko.com>, svn-src-head@freebsd.org, Alexander Kabaev <kabaev@gmail.com>
Subject:   Re: svn commit: r260898 - head/sys/kern
Message-ID:  <D04BF613-A78D-43B8-A22B-DA8F72D22430@yahoo.com>
In-Reply-To: <201401211126.18930.jhb@freebsd.org>
References:  <201401200159.s0K1xa5X012123@svn.freebsd.org> <1536225.gsjt6oXMt2@pippin.baldwin.cx> <20140120171844.69e065fb@kan.dyndns.org> <201401211126.18930.jhb@freebsd.org>

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On Jan 21, 2014, at 9:26 AM, John Baldwin <jhb@freebsd.org> wrote:

> On Monday, January 20, 2014 5:18:44 pm Alexander Kabaev wrote:
>> On Mon, 20 Jan 2014 11:32:29 -0500
>> John Baldwin <jhb@freebsd.org> wrote:
>>=20
>>> On Sunday 19 January 2014 18:18:03 Rui Paulo wrote:
>>>> On 19 Jan 2014, at 17:59, Neel Natu <neel@FreeBSD.org> wrote:
>>>>> Author: neel
>>>>> Date: Mon Jan 20 01:59:35 2014
>>>>> New Revision: 260898
>>>>> URL: http://svnweb.freebsd.org/changeset/base/260898
>>>>>=20
>>>>> Log:
>>>>> Bump up WITNESS_COUNT from 1024 to 1536 so there are sufficient
>>>>> entries for
>>>>> WITNESS to actually work.
>>>>=20
>>>> This value should be automatically tuned...
>>>=20
>>> How do you propose to do so?  This is the count of locks initialized
>>> before witness' own SYSINIT is executed and the array it sizes is
>>> allocated statically at compile time.  This used to not be a static
>>> array, but an intrusive list embedded in locks themselves, but we
>>> decided to shave a pointer off of each lock that was only used for
>>> that and to use a statically sized table instead.
>>>=20
>>> --=20
>>> John Baldwin
>>=20
>> As <CONSTANT1> + <CONSTANT2> * MAXCPU, as evidently most recent
>> overflows reported were caused by jacking MAXCPU up from its default
>> value?=20
>=20
> If raising MAXCPU changes the number of unique lock names used, then =
the
> locks are named incorrectly.  We don't use the 'pid' in the name for
> PROC_LOCK precisely so that WITNESS will treat them all the same so
> that if if it learns a lock order for pid 37 it enforces the same lock
> order for pid 38.  Device locks should follow a similar rule.  They
> should generally not include the device name (and in some cases they
> really shouldn't even have the driver name).

Why shouldn=92t they have a driver and device name?  Wouldn=92t it help =
identify
possible deadlocks from driver instances calling into each other?

Scott




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