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Ping. Cary, is this alright to commit? * options.h (-z,text_unlikely_segment): New option. * layout.cc (Layout::layout): Create new output section for .text.unlikely sections with the new option. (Layout::segment_precedes): Check for the new option when segment flags match. * testsuite/text_unlikely_segment.cc: New test source. * testsuite/text_unlikely_segment.sh: New test script. * testsuite/Makefile.am (text_unlikely_segment): New test. On Thu, Oct 5, 2017 at 4:41 PM, Sriraman Tallam <tmsriram@google.com> wrote: > On Thu, Oct 5, 2017 at 4:41 PM, H.J. Lu <hjl.tools@gmail.com> wrote: >> On 10/5/17, Sriraman Tallam <tmsriram@google.com> wrote: >>> On Wed, Oct 4, 2017 at 5:12 PM, H.J. Lu <hjl.tools@gmail.com> wrote: >>>> On 10/4/17, Sriraman Tallam <tmsriram@google.com> wrote: >>>>> Hi, >>>>> >>>>> This patch adds an option to gold to create a new ELF segment for >>>>> code determined unlikely by the compiler. Currently, this can be done >>>>> with a linker plugin but I was wondering if it is fine to have this >>>>> support in gold with an option for ease of use. >>>>> >>>>> The advantages of doing this are: >>>>> >>>>> * We could only map the hot segment to huge pages to keep iTLB misses >>>>> low >>>>> * We could munlock the unlikely segment >>>>> >>>>> Is this alright? >>>>> >>>>> ChangeLog entry: >>>>> >>>>> * options.h (text_unlikely_segment): New option. >>>>> * layout.cc (Layout::layout): Create new output section >>>>> for .text.unlikely sections with the new option. >>>>> (Layout::segment_precedes): Check for the new option >>>>> when segment flags match. >>>>> >>>>> Patch attached. >>>>> >>>> >>>> This is an interesting approach. Do you have some performace >>>> numbers? >>> >>> With function re-ordering of hot code, segment splitting and mapping >>> only hot code to huge pages, we see a reduction in iTLB misses >>> translating to performance improvements of 0.5 to 1% on some of our >>> benchmarks. >> >> Please include this info in your commit log. >> >>>> >>>> 2 Comments: >>>> >>>> 1. I'd prefer "-z text-unlikely-segment" with '-', instead of '_'. >>>> 2. Need a testcase. >>> >>> Done and patch attached. >>> >> >> LGTM. But I can't approve it. > > Np, thanks! > > Sri > >> >> Thanks. >> >> -- >> H.J.
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