Messages in this thread | | | Date | Tue, 29 Jul 1997 04:04:30 -0400 (EDT) | From | "Albert D. Cahalan" <> | Subject | Re: Interesting pentium-memcpy results |
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Chris Evans (chris@ferret.lmh.ox.ac.uk) writes:
> I just compared 2.1.46 vs. 2.1.46+pentium memcpy patch, > and interestingly enough found that the UNIX byte benchmarks > tended to _drop_ a fair bit, with the exception of process > creation and execl throughput. (Note that I only ran the > basic 'system' tests - TCP bandwidth etc. to be determined > when I find the newer benchmarks) > > This is most interesting since I used to swear by the patch. > > It does however show us that there still is performance to > be gained. I presume the process creation test will be using > fork() which does a lot of memcpy'ing of various process > credentials in kernel space.
I think it shows that the memcpy size test is significant. Perhaps the FPU is best used only when explicitly requested for large operations. That would mean page clearing I guess.
big_aligned_memcpy() and big_aligned_clear() perhaps? For 512 bytes and up, optimized for each arch.
There may be a conflict with the user-space version. With both the kernel and apps abusing the FPU for memcpy, the FPU must be restored too often.
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