llvm-project/compiler-rt/test/xray
Dean Michael Berris 504b0c28f3 [XRay][compiler-rt] Coalesce calls to mprotect to reduce patching overhead
Summary:
Before this change, XRay would conservatively patch sections of the code
one sled at a time. Upon testing/profiling, this turns out to take an
inordinate amount of time and cycles. For an instrumented clang binary,
the cycles spent both in the patching/unpatching routine constituted 4%
of the cycles -- this didn't count the time spent in the kernel while
performing the mprotect calls in quick succession.

With this change, we're coalescing the number of calls to mprotect from
being linear to the number of instrumentation points, to now being a
lower constant when patching all the sleds through `__xray_patch()` or
`__xray_unpatch()`. In the case of calling `__xray_patch_function()` or
`__xray_unpatch_function()` we're now doing an mprotect call once for
all the sleds for that function (reduction of at least 2x calls to
mprotect).

Reviewers: kpw, eizan

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D41153

llvm-svn: 320664
2017-12-14 02:51:20 +00:00
..
TestCases/Linux [XRay][compiler-rt] Coalesce calls to mprotect to reduce patching overhead 2017-12-14 02:51:20 +00:00
Unit [XRay][compiler-rt] Enable the XRay compiler-rt unit tests. 2017-08-31 00:50:12 +00:00
CMakeLists.txt [XRay][compiler-rt] XRay Flight Data Recorder Mode 2017-01-25 03:50:46 +00:00
lit.cfg Revert "[XRay][darwin] Initial XRay in Darwin Support" 2017-11-10 07:00:55 +00:00
lit.site.cfg.in [XRay][compiler-rt] Enable the XRay compiler-rt unit tests. 2017-08-31 00:50:12 +00:00