8dbc450f76
sparc: VDSO improvements I started out on these changes with the goal of improving perf annotations when the VDSO is in use. Due to lack of inlining the helper functions are typically hit when profiling instead of __vdso_gettimeoday() or __vdso_vclock_gettime(). The only symbols available by default are the dyanmic symbols, which therefore doesn't cover the helper functions. So the perf output looks terrible, because the symbols cannot be resolved and all show up as "Unknown". The sparc VDSO code forces no inlining because of the way the simplistic %tick register read code patching works. So fixing that was the first order of business. Tricks were taken from how x86 implements alternates. The crucial factor is that if you want to refer to locations (for the original and patch instruction(s)) you have to do so in a way that is resolvable at link time even for a shared object. So you have to do this by storing PC-relative values, and not in executable sections. Next, we sanitize the Makefile so that the cflags et al. make more sense. And LDFLAGS are applied actually to invocations of LD instead of CC. We also add some sanity checking, specifically in a post-link check that makes sure we don't have any unexpected unresolved symbols in the VDSO. This is essential because the dynamic linker cannot resolve symbols in the VDSO because it cannot write to it. Finally some very minor optimizations are preformed to the vclock_gettime.c code. One thing which is tricky with this code on sparc is that struct timeval and struct timespec are layed out differently on 64-bit. This is because, unlike other architectures, sparc defined suseconds_t as 'int' even on 64-bit. This is why we have all of the "union" tstv_t" business and the weird assignments in __vdso_gettimeofday(). Performance wise we do gain some cycle shere, specifically here are cycle counts for a user application calling gettimeofday(): no-VDSO VDSO-orig VDSO-new ================================================ 64-bit 853 cycles 112 cycles 125 cycles 32-bit 849 cycles 134 cycles 141 cycles These results are with current glibc sources. To get better we'd need to implement this in assembler, and I might just do that at some point. Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.