Add options COMPACT to produce smaller kernel
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Authored by mjg on Nov 14 2020, 6:51 PM.

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kib
markj

Summary

This adds __aligned_if_not_compact and converts __exclusive_cache_line to use it. It retains the section annotation, I may whack it.

I'm not interested in arguing about the name, propose something else and I'll rename. Alternatively, write your own patch and I'll use it in D27185

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rS FreeBSD src repository - subversion

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Buildable 34797

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mjg created this revision.Nov 14 2020, 6:51 PM

Herald added a subscriber: imp. · View Herald TranscriptNov 14 2020, 6:51 PM

mjg requested review of this revision.Nov 14 2020, 6:51 PM

Harbormaster completed remote builds in B34797: Diff 79552.Nov 14 2020, 6:51 PM

mjg edited the summary of this revision. (Show Details)Nov 14 2020, 6:54 PM

kib added inline comments.Nov 14 2020, 7:47 PM

sys/conf/options
1019	Not specifying file name means that option is stored in opt_compact.h, but you never include it. I strongly suggest putting it in opt_global.h.
sys/sys/cdefs.h
244	This header is also used for userspace, and COMPACT is clearly is in user namespace. Perhaps we need to use protected name for the option, like __COMPACT.

mjg added inline comments.Nov 16 2020, 1:31 AM

sys/sys/cdefs.h
244	so that would be __COMPACT put in the config? Looks like some form of prefixing would be warranted for cases like this. I don't think the COMPACT option (with whatever name) is worth introducing at this time if it goes beyond the few lines (+ fixups) I posted here.

kib added inline comments.Nov 17 2020, 2:02 AM

sys/sys/cdefs.h
244	I think it should go somewhere in systm.h or similar. Then it could be COMPACT without prefix. I do think that COMPAT is worth it, even if such small for now. It is first step, and I expect that it will be taken from this quite fast. It is long overdue.

So put together the following. This runs into further issues as users have to explicitly include opt_global to get the macro, so I think this is just too error prone in this form.

That said, I don't intend to work on this any further. If you want to see this option in you will have to take over or get someone else to do it.

This looks fine to me as the first step.

There is no need to manually include opt_global.h, it is automatically pre-included by the build infrastructure: -include /usr/home/kostik/work/DEV/src/sys/amd64/compile/GENERIC/opt_global.h.

I wonder how much more can we pack in the first commit, e.g. mtx_padalign can be converted to __aligned_if_not_compact.