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Date: Wed, 04 Nov 2009 14:00:33 -0500 From: Jeff Moyer <jmoyer@...hat.com> To: Vivek Goyal <vgoyal@...hat.com> Cc: linux-kernel@...r.kernel.org, jens.axboe@...cle.com, nauman@...gle.com, dpshah@...gle.com, lizf@...fujitsu.com, ryov@...inux.co.jp, fernando@....ntt.co.jp, s-uchida@...jp.nec.com, taka@...inux.co.jp, guijianfeng@...fujitsu.com, balbir@...ux.vnet.ibm.com, righi.andrea@...il.com, m-ikeda@...jp.nec.com, akpm@...ux-foundation.org, riel@...hat.com, kamezawa.hiroyu@...fujitsu.com Subject: Re: [PATCH 15/20] blkio: Take care of preemptions across groups Vivek Goyal <vgoyal@...hat.com> writes: > +static bool cfq_should_preempt_group(struct cfq_data *cfqd, > + struct cfq_queue *cfqq, struct cfq_queue *new_cfqq) > +{ > + struct cfq_entity *cfqe = &cfqq->entity; > + struct cfq_entity *new_cfqe = &new_cfqq->entity; > + > + if (cfqq_to_cfqg(cfqq) != &cfqd->root_group) > + cfqe = parent_entity(&cfqq->entity); > + > + if (cfqq_to_cfqg(new_cfqq) != &cfqd->root_group) > + new_cfqe = parent_entity(&new_cfqq->entity); > + > + /* > + * Allow an RT request to pre-empt an ongoing non-RT cfqq timeslice. > + */ > + > + if (new_cfqe->ioprio_class == IOPRIO_CLASS_RT > + && cfqe->ioprio_class != IOPRIO_CLASS_RT) > + return true; > + /* > + * Allow an BE request to pre-empt an ongoing IDLE clas timeslice. > + */ > + > + if (new_cfqe->ioprio_class == IOPRIO_CLASS_BE > + && cfqe->ioprio_class == IOPRIO_CLASS_IDLE) > + return true; > + > + return false; > +} What was the motivation for this? It seems like this would really break isolation. What if one group has all RT priority tasks, will it starve out the other groups? Cheers, Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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