[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v12 13/23] x86: refactor psr: CDP: implement CPU init flow.
>>> On 04.07.17 at 03:40, <yi.y.sun@xxxxxxxxxxxxxxx> wrote: > On 17-06-30 03:18:53, Jan Beulich wrote: >> >>> Yi Sun <yi.y.sun@xxxxxxxxxxxxxxx> 06/30/17 10:05 AM >>> >> >On 17-06-30 01:33:02, Jan Beulich wrote: >> >> >>> Yi Sun <yi.y.sun@xxxxxxxxxxxxxxx> 06/30/17 9:01 AM >>> >> >> >This accords to spec: >> >> >"For CDP operations, COS_MAX_CDP is equal to (CPUID.(EAX=10H, >> >> >ECX=1):EDX.COS_MAX_CAT >>1)." >> >> > >> >> >HW should make sure it is even number. >> >> >> >> And how about someone using the command line option to shrink the to be >> >> used set? >> >> >> >Good question. The command line option saved in 'opt_cos_max', even it is >> >not even number and less than 'EDX.COS_MAX_CAT' so that the 'cos_max' here >> >is >> >same as it, the right shift operation does not cause any issue I think. >> > >> >The description in docs/misc/xen-command-line.markdown is clear that "the >> >cos_max >> >in use will automatically reduce to half when CDP is enabled". E.g. >> >'opt_cos_max' >> >is 5, then we get 2 for CDP. I think user should be aware of this by >> >reading the >> >markdown file. >> >> I don't really follow all this argumentation - what's the problem of simply >> subtracting >> 1 before doing the shift? Talking of which - isn't the general cos_max > 1 >> also > > There will be problem if we substract 1 before doing the shift for the even > number. E.g. the original cos_max is 2, (2-1)>>1 will be 0. That is not we > want. For the odd number, direct right shift is good too. E.g. the original > cos_max is 3, 3 >> 1 is 1 which is what we want. What we want is raw CDP 0 unusable 1 0 2 0 3 1 4 1 5 2 6 2 Other than what you say, for original cos_max = 2 we indeed need to convert it to 0, or else CDP would use indexes 2 ( = 1 * 2 + 0) and 3 ( = 1 * 2 + 1), exceeding the mandated upper bound. >> insufficient for the CDP case? > > We do not need check if cos_max > 1 because the 'cos_max = 0' works for us. > That means only COS ID 0 can be used. You can see, we use "cos <= cos_max" to > find COS ID. Of course, the ID 0 saves the default value which cannot be > overwritten. Please see the (current) check in init_psr_cat(), which your series moves into init_psr(). Logically in the CDP case we should require cos_max >= 3 to have at least one usable COS ID. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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