Hi Ingo, On Sun, Feb 11, 2018 at 08:13:12PM +0100, Ingo Molnar wrote: > Could you please measure the PTI kernel vs. vanilla kernel? Okay, did that, here is the data. The test machine is a Xeon E5-1620v2, which is Ivy Bridge based (no PCIE) and has 4C/8T. I ran the 2 tests you suggested: * Test-1: perf stat --null --sync --repeat 10 perf bench sched messaging -g 20 * Test-2: perf stat --null --sync --repeat 10 perf bench sched messaging -g 20 -t The tests ran on these kernels: * tip-32-pae: current top of tip/x86-tip-for-linus branch, compiled as a 32 bit kernel with PAE (commit b2ac58f90540e39324e7a29a7ad471407ae0bf48) * pti-32-pae: Same as above with my patches on-top, as on git://git.kernel.org/pub/scm/linux/kernel/git/joro/linux.git pti-x32-v2 compiled as a 32 bit kernel with PAE (commit dbb0074f778b396a11e0c897fef9d0c4583e7ccb) * pti-off-64: current top of tip/x86-tip-for-linus branch, compiled as a 64 bit kernel, booted with pti=off (commit b2ac58f90540e39324e7a29a7ad471407ae0bf48) * pti-on-64: current top of tip/x86-tip-for-linus branch, compiled as a 64 bit kernel, booted with pti=on (commit b2ac58f90540e39324e7a29a7ad471407ae0bf48) Results are: | Test-1 | Test-2 ------------+--------------------+----------------- tip-32-pae | 0.28s (+-0.44%) | 0.27s (+-2.15%) ------------+--------------------+----------------- pti-32-pae | 0.44s (+-0.40%) | 0.42s (+-0.48%) ------------+--------------------+----------------- pti-off-64 | 0.24s (+-0.40%) | 0.25s (+-1.31%) ------------+--------------------+----------------- pti-on-64 | 0.30s (+-0.47%) | 0.31s (+-0.95%) On 32 bit with PTI enabled the test needs 157% (non-threaded) and 156% (threaded) of time compared to the non-PTI baseline. On 64 bit these numbers are 125% (non-threaded) and 124% (threaded). The pti-32-pae kernel still used 'rep movsb' in the entry code. I replaced that with 'rep movsl' and measured again, but overhead is still around 152%. I also measured cycles with 'perf record' to see where the additional time is spent. The report showed around 25% in entry_SYSENTER_32 for the pti-32-pae kernel. The same report on the tip-32-pae kernel shows around 2.5% for the same symbol. The entry_SYSENTER_32 path does no stack-copy on entry (it only push/pops 8 bytes for the cr3 switch), but one full pt_regs copy on exit. The exit-path was easy to optimize, I got it to the point where it only copied 8 bytes to the entry stack (flags and eax). This way I got the 'perf report' numbers for entry_SYSENTER_32 down to around 20%, but the overall numbers for Test-1 and Test-2 are still at around 150% of the baseline. So it seems that most of the additional time is actually spent switching the cr3s. Regards, Joerg -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
