On Wed, May 30, 2012 at 10:35 PM, Mulyadi Santosa <mulyadi.santosa@xxxxxxxxx> wrote: > Hi... > > On Thu, May 31, 2012 at 4:44 AM, Abu Rasheda <rcpilot2010@xxxxxxxxx> wrote: >> 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 copy_from_user is more efficient when copy data is small, >> why it is so ? > > you meant, the bigger the buffer, the fewer the instructions, right? yes > > Not sure why, but I am sure it will reach some peak point. > > Anyway, you did kmalloc and then kfree()? I think that's why...bigger > buffer will grab large chunk from slab...and again likely it's > physically contigous. Also, it will be placed in the same cache line. > > Whereas the smaller one....will hit allocate/free cycle more...thus > flushing the L1/L2 cache even more. It seems to be doing opposite, bigger the allocation / copy longer stall is. _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
