Messages in this thread | | | Date | Fri, 4 Sep 2015 22:52:40 +0300 | From | Yury Norov <> | Subject | Re: [RFC PATCH] arm64: cpuinfo: reduce cache contention on update_{feature}_support |
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On Fri, Sep 04, 2015 at 05:40:57PM +0100, Suzuki K. Poulose wrote: > On 04/09/15 17:04, Yury Norov wrote: > >This patch is on top of https://lkml.org/lkml/2015/9/2/413 > > > >In master, there's only a single function - > > update_mixed_endian_el0_support > >And similar function is on review mentioned above. > > > >The algorithm for them is like this: > > - there's system-wide boolean marker for the feature that is > > initially enabled; > > - there's also updater for the feature that may disable it > > system-widely if feature is not supported on current CPU. > > - updater is called for each CPU on bootup. > > > >The problem is the way updater does its work. On each CPU, it > >unconditionally updates system-wide marker. For multi-core > >system it makes CPU issue invalidate message for a cache > >line containing marker. This invalidate increases cache > >contention for nothing, because there's a single marker reset > >that is really needed, and the others are useless. > > > >If the number of system-wide markers of this sort will grow, > >it may become a trouble on large-scale SOCs. The fix is trivial, > >though: do system-wide marker update conditionally, and preserve > >corresponding cache line in shared state for all update() calls, > >except, probably, one. > > As I have mentioned already, this patch (and the per feature functions) > won't be needed once we merge my series (which is waiting for the merge > window to see the public lights) >
OK. Than waiting for your patchset.
BR, Yury
> Cheers > Suzuki
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