Re: [PATCH v3] x86/vdso: Handle clock_gettime(CLOCK_TAI) in vDSO
From: Florian Weimer
Date: Thu Sep 13 2018 - 04:07:23 EST
On 09/12/2018 07:11 PM, Andy Lutomirski wrote:
The multiplexer interfaces need much more surgery and talking about futex,
Thereâs also the issue of how much the speedup matters. For futex, maybe a better interface saves 3ns, but a futex syscall is hundreds of ns. clock_gettime() is called at high frequency and can be ~25ns. Saving a few ns is a bigger deal.
we'd need to sit down with quite some people and identify the things they
actually care about before just splitting it up and keeping the existing
overloaded trainwreck the same.
My concern is that the userspace system call wrappers currently do not
know how many arguments the individual operations take and what types
the arguments have (hence the âtype-polymorphicâ nature I mentioned).
This could be a problem for on-stack argument passing (where you might
read values beyond the end of the stack, and glibc avoids that most of
the time by having enough cruft on the stack), and for architectures
which pass pointers and integers in different registers (like some m68k
ABIs do for the return value).