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Ciaran McCreesh wrote: |
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| On Wed, 22 Sep 2004 21:40:39 -0400 John Richard Moser |
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| <nigelenki@×××××××.net> wrote: |
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| | | Personally, I would be *very* wary about giving our x86 users a 5% |
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| | | performance hit |
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| | |
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| | 1. Where are you getting 5% from? |
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| I did some quick measurements on vim's test suite with and without |
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| -fstack-protector. The value varies per app, of course, but vim's regex |
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| stuff was taking a ~10% hit (not surprising) and the file ops were |
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| affected considerably less. *shrug* depends upon the app, of course. |
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Mmm, interesting. |
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Because SSP's protections are not generally applied (-fstack-protector |
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only affects functions with strings), it's difficult to measure I guess. |
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| | 2. What context is this "Performance" hit in? gcc would take a |
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| | "performance" hit because it eats 100% CPU; most nothing else would |
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| | take a "performance" hit unless the *overhead* pulled CPU usage up to |
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| | 100% for a time. |
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| Well, performance when a box is at low load is of no interest... |
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Which is 99% of the time of course. :) Hell if your box is running at |
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80% load performance hit is of no interest (although adding enough for |
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it to run at 80% load instead of 1% is bad). |
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| | I guess this is the point where I have to ebuild unpack nbyte and |
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| | generate SSP benchmarks. Why oh why didn't I bench ssp when I was |
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| | doing PIC? |
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| Note that some kinds of benchmarks, such as integer op tests, won't |
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| be affected at all by SSP. Certain kinds of string handling, on the |
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| other hand, will be hit really badly. Better to pick an app and |
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| benchmark it than running dedicated benchmarkers. |
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Heh. True, it's too specific to quantify I guess. |
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The impact is also less with large functions. If you have a 3 |
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instruction function, the extra SSP instructions are bigger than the |
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damn function; if you have a function made of 150 lines of C code, |
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obviously that's going to have little to no impact. |
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- -- |
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