Date: Thu, 23 Feb 2012 07:44:21 +0530 From: "Desai, Kashyap" <Kashyap.Desai@lsi.com> To: Chuck Swiger <cswiger@mac.com> Cc: "freebsd-scsi@freebsd.org" <freebsd-scsi@freebsd.org>, freebsd-stable <freebsd-stable@freebsd.org>, "McConnell, Stephen" <Stephen.McConnell@lsi.com> Subject: RE: mpslsi0 : Trying sleep, but thread marked as sleeping prohibited Message-ID: <B2FD678A64EAAD45B089B123FDFC3ED72B96D34855@inbmail01.lsi.com> In-Reply-To: <FDA8B243-6E6F-458A-8B93-D863EC9785B2@mac.com> References: <B2FD678A64EAAD45B089B123FDFC3ED72B96D34836@inbmail01.lsi.com> <20120222191519.GT55074@deviant.kiev.zoral.com.ua> <B2FD678A64EAAD45B089B123FDFC3ED72B96D34854@inbmail01.lsi.com> <FDA8B243-6E6F-458A-8B93-D863EC9785B2@mac.com>
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> -----Original Message-----
> From: Chuck Swiger [mailto:cswiger@mac.com]
> Sent: Thursday, February 23, 2012 6:21 AM
> To: Desai, Kashyap
> Cc: freebsd-scsi@freebsd.org; freebsd-stable; McConnell, Stephen
> Subject: Re: mpslsi0 : Trying sleep, but thread marked as sleeping
> prohibited
>=20
> On Feb 22, 2012, at 4:22 PM, Desai, Kashyap wrote:
> > Just curious to know, What is a reason that thread can do blocking
> sleep but can't do unbounded sleep ?
>=20
> When you block, the scheduler can run other threads and only needs to
> wake up and run your thread after the blocking condition is completed.
>=20
> However, you don't want to busy-wait in a spin lock/mutex for any
> lengthy period of time. If your thread was allowed to do an unbounded
> sleep, especially in a fast interrupt handler context, what's going to
> wake it up? An NMI like the reset button [1]? :-)
When I started working on freebsd, first thing I noticed was ISR in freebsd=
are thread. (special thread). But at least not like linux where we don't h=
ave pid associate with ISR.
So In Freebsd we will have thread id for related isr routine.
Consider that fact, Even in fast interrupts handler context we should be ab=
le to sleep. (e.a pause("mps_pause", (hz/1000));)
Schedule can put thread into wait_queue and eventually when wait condition =
meet, thread will be wake by OS.
I mean if we can sleep in fast interrupt handler using mtx_ call, why not m=
sleep/pause ?
Sorry if I am extending this conversation. I really appreciate kind of help=
from freebsd forum.!
` Kashyap
>=20
> Regards,
> --
> -Chuck
>=20
> [1]: Well, you could also call STI to permit clock interrupts or
> something else to fire an interrupt, but then your interrupt handler
> needs to be re-entrant. (And watch out for multiple nested interrupts
> blowing out the available stack space....)
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