Date: Mon, 27 Feb 2012 23:17:07 +0530 From: "Desai, Kashyap" <Kashyap.Desai@lsi.com> To: John Baldwin <jhb@freebsd.org>, "freebsd-stable@freebsd.org" <freebsd-stable@freebsd.org> Cc: Konstantin Belousov <kostikbel@gmail.com>, "freebsd-scsi@freebsd.org" <freebsd-scsi@freebsd.org>, "Justin T. Gibbs" <gibbs@freebsd.org>, "Kenneth D. Merry" <ken@freebsd.org>, "McConnell, Stephen" <Stephen.McConnell@lsi.com> Subject: RE: mpslsi0 : Trying sleep, but thread marked as sleeping prohibited Message-ID: <B2FD678A64EAAD45B089B123FDFC3ED72B96D34AF2@inbmail01.lsi.com> In-Reply-To: <201202230958.05667.jhb@freebsd.org> References: <B2FD678A64EAAD45B089B123FDFC3ED72B96D34836@inbmail01.lsi.com> <20120223092457.GB55074@deviant.kiev.zoral.com.ua> <B2FD678A64EAAD45B089B123FDFC3ED72B96D3492A@inbmail01.lsi.com> <201202230958.05667.jhb@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
> -----Original Message----- > From: John Baldwin [mailto:jhb@freebsd.org] > Sent: Thursday, February 23, 2012 8:28 PM > To: freebsd-stable@freebsd.org > Cc: Desai, Kashyap; Konstantin Belousov; freebsd-scsi@freebsd.org; > Kenneth D. Merry; Justin T. Gibbs; McConnell, Stephen > Subject: Re: mpslsi0 : Trying sleep, but thread marked as sleeping > prohibited >=20 > On Thursday, February 23, 2012 8:22:07 am Desai, Kashyap wrote: > > > > > -----Original Message----- > > > From: Konstantin Belousov [mailto:kostikbel@gmail.com] > > > Sent: Thursday, February 23, 2012 2:55 PM > > > To: Desai, Kashyap > > > Cc: freebsd-scsi@freebsd.org; freebsd-stable; Justin T. Gibbs; > Kenneth > > > D. Merry; McConnell, Stephen > > > Subject: Re: mpslsi0 : Trying sleep, but thread marked as sleeping > > > prohibited > > > > > > On Thu, Feb 23, 2012 at 05:52:12AM +0530, Desai, Kashyap wrote: > > > > > > > > > > > > > -----Original Message----- > > > > > From: Konstantin Belousov [mailto:kostikbel@gmail.com] > > > > > Sent: Thursday, February 23, 2012 12:45 AM > > > > > To: Desai, Kashyap > > > > > Cc: freebsd-scsi@freebsd.org; freebsd-stable; Justin T. Gibbs; > > > > > Kenneth D. Merry; McConnell, Stephen > > > > > Subject: Re: mpslsi0 : Trying sleep, but thread marked as > sleeping > > > > > prohibited > > > > > > > > > > On Wed, Feb 22, 2012 at 07:36:42PM +0530, Desai, Kashyap wrote: > > > > > > Hi, > > > > > > > > > > > > I am doing some code changes in mps dirver. While working on > those > > > > > changes, I come to know about something which is new to me. > > > > > > Some expert help is required to clarify my doubt. > > > > > > > > > > > > 1. When any irq is register with FreeBSD OS, it sets " > > > TDP_NOSLEEPING" > > > > > > pflag. It means though irq in freebsd is treated as thread, We > > > > > > cannot > > > > > sleep in IRQ because of " "TDP_NOSLEEPING " set. > > > > > > 2. In mps driver we have below code snippet in ISR routine. > > > > > > > > > > > > > > > > > > mps_dprint(sc, MPS_TRACE, "%s\n", __func__); > > > > > > mps_lock(sc); > > > > > > mps_intr_locked(data); > > > > > > mps_unlock(sc); > > > > > > > > > > > > I wonder why there is no issue with above code ? Theoretical > we > > > > > > cannot sleep in ISR. (as explained in #1) Any thoughts ? > > > > > > > > > > > > > > > > > > 3. I recently added few place msleep() instead of DELAY in ISR > > > > > > context and I see " Trying sleep, but thread marked as > sleeping > > > prohibited". > > > > > > > > > > > FreeBSD has several basic ways to prevent a thread from > executing on > > > > > CPU. > > > > > They mostly fall into two categories: bounded sleep, sometimes > > > > > called blocking, and unbounded sleep, usually abbreviated as > sleep. > > > > > The bounded there refers to amount of code executed by other > thread > > > > > that hold resource preventing blocked thread from making a > progress. > > > > > > > > > > Examples of the blocking primitives are mutexes, rw locks and rm > > > locks. > > > > > The blocking is not counted as sleeping, so interrupt threads, > which > > > > > are designated as non-sleeping, still can lock mutexes. > > > > Thanks for the tech help. . > > > > > > > > As per you comment, So now I understood as "TDP_NOSLEEPING" is > only > > > > for unbounded sleep restriction. Just curious to know, What is a > > > > reason that thread can do blocking sleep but can't do unbounded > sleep > > > > ? Since technically we introduced sleeping restriction on > interrupt > > > > thread is to avoid starvation and that can be fit with either of > the > > > > sleep type. Is this not true ? > > > No, not to avoid starvation. > > > > > > The intent of the blocking primitives is to acquire resources for > > > limited amount of time. In other words, you never take a mutex for > > > undefinitely long computation process. On the other hand, msleep > sleep > > > usually has no limitations. > > > > I got same reply from Ed Schouten. I agree and understood your note. > Thanks > for poring knowledge on this area. > > _but_ only query is when thread take mutex, we don't know when it will > release. So holding time of mutex is really not known. > > In case of some bad code, where thread took mutex and not release > within > short time. This can eventually match upto msleep restriction as well. > > Do we have any checks that thread took long time holding mutext ? > Similar > to linux where spinlock has been not release in some specific time, they > dump > warnings with backtrace. >=20 > We don't allow code to do unbounded sleeps while holding mutexes either, > and > WITNESS warns about doing so. That ensures that barring an infinite > loop-type > bug, mutexes should be held for a bounded amount of time. Thanks. I understood this concept now. Really helpful conversation. >=20 > -- > John Baldwin
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?B2FD678A64EAAD45B089B123FDFC3ED72B96D34AF2>