Hi Scotty,

On Wed, Jan 31, 2018 at 11:43:33AM -0700, Scotty Bauer wrote:

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

quoted

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.

My CPU has PCID, which can be retrieved via /proc/cpuinfo.

And the above test is run on same kernel binary, and the result is just done
between 'nopti' and no 'nopti' in kernel command line.

Thanks,
Ming
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