On Wed, May 30, 2012 at 2:44 PM, Abu Rasheda <rcpilot2010@xxxxxxxxx> wrote: > I did another experiment. > > Wrote a stand alone module and user program which does ioctl and pass > buffer to kernel module. > > User program passes a buffer through ioctl and kernel module does > kmalloc on it and calls copy_from_user, kfree and return. Test program > send 120 gigabyte data to module. > > If I pass 1k buffer per call, I get > > 115,396,349,819 instructions # 0.90 insns per cycle > [95.00%] > > as I increase size of buffer, insns per cycle keep decreasing. Here is the data: > > 1k 0.90 insns per cycle > 8k 0.43 insns per cycle > 43k 0.18 insns per cycle > 100k 0.08 insns per cycle > > Showing that cop_from_user is more efficient when copy data is small, > why it is so ? Did another experiment: User program sending 43k and allocating 43k after entering ioctl and copy_from_user smaller portion in each call to copy_from_user: ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- copy_from_user 0.25k at a time 0.56 insns per cycle copy_from_user 0.50k at a time 0.42 insns per cycle copy_from_user 1.00k at a time 0.36 insns per cycle copy_from_user 2.00k at a time 0.29 insns per cycle copy_from_user 3.00k at a time 0.26 insns per cycle copy_from_user 4.00k at a time 0.23 insns per cycle copy_from_user 8.00k at a time 0.21 insns per cycle copy_from_user 16.00k at a time 0.19 insns per cycle User program sending 43k, allocating smaller chunk and sending that chunk to call to copy_from_user: -------------------------------------------------------------------------------------------------------------------------------------------------------------- Allocated 0.25k and copy_from_user 0.25k at a time 1.04 insns per cycle Allocated 0.50k and copy_from_user 0.50k at a time 0.90 insns per cycle Allocated 1.00k and copy_from_user 1.00k at a time 0.79 insns per cycle Allocated 2.00k and copy_from_user 2.00k at a time 0.67 insns per cycle Allocated 4.00k and copy_from_user 4.00k at a time 0.53 insns per cycle Allocated 8.00k and copy_from_user 8.00k at a time 0.42 insns per cycle Allocated 16.00k and copy_from_user 16.00k at a time 0.33 insns per cycle Allocated 32.00k and copy_from_user 32.00k at a time 0.22 insns per cycle _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
