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Date: Fri, 3 Apr 2015 21:47:13 +0200 From: Luca Abeni <luca.abeni@...tn.it> To: Henrik Austad <henrik@...tad.us> Cc: Zhiqiang Zhang <zhangzhiqiang.zhang@...wei.com>, juri.lelli@....com, linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org Subject: Re: [PATCH] Documentation/scheduler/sched-deadline.txt: correct definition of density as C_i/min{D_i,P_i} Hi Henrik, On Fri, 3 Apr 2015 19:57:37 +0200 Henrik Austad <henrik@...tad.us> wrote: [...] > > C_i/min{D_i,T_i},where T_i is not referred before, should be > > substituted by C_i/min{D_i,P_i}. > > Actually, I'd prefer we use T_i to describe the period and not P > because: > > - P is easy to confuse with priority - which has _nothing_ to do with > deadline scheduling > > - I was going to state that "the litterature is consistent in its > usage of 'T_i' for task i's period". But then I dived through some of > the books and of course it isn't. Buttazzo use T, Jane Liu use P and > so on. However, I state that *most* litterature use T_i do denote the > period of task i. Burns & Davis has a nice summary of RT-litterature > [1]. I think literature is more or less equally divided between "P" and "T" (I suspect I personally used different letters in different papers :) > So I'd rather prefer a s/P_i/T_i/ throughout the text. > > I realise that I've reviewed quite a lot of this, and I have some > vague memories of this being discussed earlier, Juri? Luca? I remember there was a discussion (and I seem to remember that the symbol used for the period was changed at least one time, but I might be wrong), but I do not remember the details. Next week I'll have some time for working on this; I'll search the old emails and I'll try to reconstruct the discussion. [...] > > - a task as C_i/min{D_i,T_i}, and EDF is able to respect all the > > deadlines > > - of all the tasks running on a CPU if the sum sum_i > > C_i/min{D_i,T_i} of the > > + a task as C_i/min{D_i,P_i}, and EDF is able to respect all the > > deadlines > > + of all the tasks running on a CPU if the sum sum_i > > C_i/min{D_i,P_i} of the > > My argument for T_i vs. P_i aside, I do agree that we should not use > T_i here whilst using P_i in other places. We should strive to be > internally consistent above all else. I fully agree with this ;-) Luca -- 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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