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Re: [PATCH v2] Single threaded stdio optimization
On Fri, Jun 30, 2017 at 4:18 PM, Torvald Riegel <firstname.lastname@example.org> wrote:
> On Fri, 2017-06-30 at 13:15 +0100, Szabolcs Nagy wrote:
>> on a particular x86_64 cpu with particular loop count:
>> time $orig/lib64/ld-2.25.90.so --library-path $orig/lib64 ./getchar
>> 5.89user 0.07system 0:05.98elapsed 99%CPU (0avgtext+0avgdata 2000maxresident)k
>> 0inputs+0outputs (0major+153minor)pagefaults 0swaps
>> time $stdio/lib64/ld-2.25.90.so --library-path $stdio/lib64 ./getchar
>> 2.66user 0.06system 0:02.73elapsed 99%CPU (0avgtext+0avgdata 2032maxresident)k
>> 0inputs+0outputs (0major+155minor)pagefaults 0swaps
> What's interesting here is that your high-level optimization is faster
> than doing the single-thread check in the low-level lock (x86 has it
> already in the low-level lock).
Isn't that the expected behaviour here ?