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Re: [tor-bugs] #27208 [Core Tor/Tor]: add API for allocating aligned memory
#27208: add API for allocating aligned memory
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Reporter: cyberpunks | Owner: (none)
Type: enhancement | Status: needs_revision
Priority: Medium | Milestone: Tor: 0.3.6.x-final
Component: Core Tor/Tor | Version:
Severity: Normal | Resolution:
Keywords: rust-wants rust | Actual Points:
Parent ID: #23882 | Points:
Reviewer: | Sponsor:
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Changes (by dgoulet):
* status: needs_review => needs_revision
Comment:
Thanks for this!
* This code uses `posix_memalign()` as the fallback if both `memalign()`
and `aligned_alloc()` aren't present. This has been added a _while_ back
so I'm not too worried about any system we currently build on today to not
have it but hey you never know... (`_POSIX_C_SOURCE >= 200112L`).
Should we add a check at configure time and fail if none of the 3
functions are present?
* I would add a `PREDICT_UNLIKELY()` around the `posix_memalign()` for
sake of "performance" :).
* I think we should make `static void *aligned_alloc...` inline in my
opinion... might need some code change from the patch but since
`tor_malloc()` is used extensively, any performance gain is good.
* More a meta-physic question: Do we really need to reroute every
`tor_malloc()` to the aligned one with alignment set to 1? In the case of
`memalign()` and `aligned_alloc()`, of what I can read from the glibc, it
will be re-routed to the normal `malloc()` if alignment is below some
minimum.
But with `posix_memalign()`, this means that every `tor_malloc()` now
needs to do a `MAX()`, which results in _always_ using `sizeof(void *)`. I
know this is very cheap CPU side but maybe we can avoid this couple of
extra cycles by simply making `tor_malloc_()` use the right alignment by
default and removing the `MAX()` ?
I know I'm arguing about nanoseconds here but `tor_malloc()` is one of
the *core* foundation of the entire code base, adding any extra work to it
is something I personally want to avoid unless it is security related.
--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/27208#comment:4>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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