Date: Thu, 4 Nov 2010 17:22:46 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-arch@freebsd.org Cc: Matthew Fleming <mdf356@gmail.com>, freebsd-usb@freebsd.org, Weongyo Jeong <weongyo.jeong@gmail.com>, freebsd-current@freebsd.org Subject: Re: [RFC] Outline of USB process integration in the kernel taskqueue system Message-ID: <201011041722.46673.jhb@freebsd.org> In-Reply-To: <201011042115.16187.hselasky@c2i.net> References: <201011012054.59551.hselasky@c2i.net> <AANLkTinoUKy6P=U7q9qEKvEviw1Z_rxvdBvUotuGuTzi@mail.gmail.com> <201011042115.16187.hselasky@c2i.net>
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On Thursday, November 04, 2010 4:15:16 pm Hans Petter Selasky wrote: > On Thursday 04 November 2010 21:11:38 Matthew Fleming wrote: > > On Thu, Nov 4, 2010 at 12:11 PM, Hans Petter Selasky <hselasky@c2i.net> > wrote: > > > On Thursday 04 November 2010 20:01:57 Matthew Fleming wrote: > > >> On Thu, Nov 4, 2010 at 11:41 AM, Hans Petter Selasky <hselasky@c2i.net> > > > > > > wrote: > > >> > On Thursday 04 November 2010 15:29:51 John Baldwin wrote: > > >> >> (and there is in Jeff's OFED branch) > > >> > > > >> > Is there a link to this branch? I would certainly have a look at his > > >> > work and re-base my patch. > > >> > > >> It's on svn.freebsd.org: > > >> > > >> http://svn.freebsd.org/viewvc/base/projects/ofed/head/sys/kern/subr_task > > >> que ue.c?view=log > > >> http://svn.freebsd.org/viewvc/base?view=revision&revision=209422 > > >> > > >> For the purpose of speed, I'm not opposed to breaking the KBI by using > > >> a doubly-linked TAILQ, but I don't think the difference will matter > > >> all that often (perhaps I'm wrong and some taskqueues have dozens of > > >> pending tasks?) > > >> > > >> Thanks, > > >> matthew > > > > > > At first look I see that I need a non-blocking version of: > > > > > > taskqueue_cancel( > > > > > > At the point in the code where these functions are called I cannot block. > > > Is this impossible to implement? > > > > It depends on whether the queue uses a MTX_SPIN or MTX_DEF. It is not > > possible to determine whether a task is running without taking the > > taskqueue lock. And it is certainly impossible to dequeue a task > > without the lock that was used to enqueue it. > > > > However, a variant that dequeued if the task was still pending, and > > returned failure otherwise (rather than sleeping) is definitely > > possible. > > I think that if a task is currently executing, then there should be a drain > method for that. I.E. two methods: One to stop and one to cancel/drain. Can > you implement this? I agree, this would also be consistent with the callout_*() API if you had both "stop()" and "drain()" methods. -- John Baldwin
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