On 2018-01-31 01:23, Ming Lei wrote:

Hi All,

After KPTI is merged, there is extra load introduced to context switch
between user space and kernel space. It is observed on my laptop that 
one
syscall takes extra ~0.15us[1] compared with 'nopti'.

IO performance is affected too, it is observed that IOPS drops by 32% 
in
my test[2] on null_blk compared with 'nopti':

randread IOPS on latest linus tree:
-------------------------------------------------
| randread IOPS     | randread IOPS with 'nopti'|
------------------------------------------------
| 928K              | 1372K                     |
------------------------------------------------

Do you know if your CPU has PCID? It would be interesting to see these 
tests on older CPUs or older kernels without PCID support.

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