Hi again! On Tue, May 29, 2012 at 8:50 PM, Abu Rasheda <rcpilot2010@xxxxxxxxx> wrote: > Hi, > > I am working on x8_64 arch. Profiled (oprofile) Linux kernel module > and notice that whole lot of cycles are spent in copy_from_user call. > I compared same flow from kernel proper and noticed that for more data > through put cycles spent in copy_from_user are much less. Kernel > proper has 1/8 cycles compared to module. (There is a user process > which keeps sending data, like iperf) > > Used perf tool to gather some statistics and found that call from kernel proper > > 185,719,857,837 cpu-cycles # 3.318 GHz > [90.01%] > 99,886,030,243 instructions # 0.54 insns per cycle > [95.00%] > 1,696,072,702 cache-references # 30.297 M/sec > [94.99%] > 786,929,244 cache-misses # 46.397 % of all cache > refs [95.00%] > 16,867,747,688 branch-instructions # 301.307 M/sec > [95.03%] > 86,752,646 branch-misses # 0.51% of all branches > [95.00%] > 5,482,768,332 bus-cycles # 97.938 M/sec > [20.08%] > 55967.269801 cpu-clock > 55981.842225 task-clock # 0.933 CPUs utilized > > and call from kernel module > > 9,388,787,678 cpu-cycles # 1.527 GHz > [89.77%] > 1,706,203,221 instructions # 0.18 insns per cycle > [94.59%] > 551,010,961 cache-references # 89.588 M/sec [94.73%] > 369,632,492 cache-misses # 67.083 % of all cache refs > [95.18%] > 291,358,658 branch-instructions # 47.372 M/sec [94.68%] > 10,291,678 branch-misses # 3.53% of all branches > [95.01%] > 582,651,999 bus-cycles # 94.733 M/sec > [20.55%] > 6112.471585 cpu-clock > 6150.490210 task-clock # 0.102 CPUs utilized > 367 page-faults # 0.000 M/sec > 367 minor-faults # 0.000 M/sec > 0 major-faults # 0.000 M/sec > 25,770 context-switches # 0.004 M/sec > 23 cpu-migrations # 0.000 M/sec How did you call from Kernel module? > > > So obviously, CPU is stalling when it is copying data and there are > more cache misses. My question is, is there a difference calling > copy_from_user from kernel proper compared to calling from LKM ? > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies@xxxxxxxxxxxxxxxxx > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies []'s -- Peter Senna Tschudin peter.senna@xxxxxxxxx gpg id: 48274C36 _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
