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