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Re: malloc, thread and alignment

Le 27/03/2015 17:38, Taylor R Campbell a écrit :
Date: Fri, 27 Mar 2015 16:30:32 +0100
   From: "Jean-Yves Migeon (NetBSD)" <>

For x86 you can look at cpuctl(8), identifycpu() uses cpuid to get this information. This is MD and varies between AMD/Intel, revisions... This requires not-so-funny tests to deduce the correct value. I don't think
   this is exposed through headers/libs for external use though.

   AFAICT !x86 platforms have nothing.

Perhaps we ought to expose it via a sysctl.

or sysconf(3)

Someone^TM should document the kernel CACHE_LINE_SIZE, coherency_unit,
COHERENCY_UNIT, and figure out what it is worthwhile to expose MI to
userland.  Obviously some systems may have different instruction and
data cache line sizes, and maybe there are more exotic possibilities,
but presumably there is a good conservative estimate for user programs
to round buffers to.  jemalloc seems to use 64 bytes unconditionally.

Maybe 64 bytes is the good conservative estimate then :) (which is not far away from reality)

Making that stuff MI "one size fits all" is tough. Looking back at cpuctl(8), I have always seen multiple possibilities for a userland binary to query that kind of information from the system: sysctl(3), sysconf(3), or specifically-crafted-structs passed to an ioctl(2) (like cpuctl). What governs the choice of an interface over another there?

(and yes, I know about proplib or Linux /sys)

Jean-Yves Migeon

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